This study was carried out under the Harran Plain Conditions in the southeastern Anatolia Project (GAP) area, on a soil group belonging to RedBrown Soils. Cotton varieties of Nazilli 84, Sayar 314 and Stoneville 453 belonging to Gossypium hirsutum L., and the F1 and F2 generations of the Sayar 314 (&) x Nazilli 84 (%) and Stoneville 453 (&) x Nazilli 84 (%) crosses were used as the material, in a completely randomized blocks experiment design with three replications. Seeds of the parents and F1 generations were planted in 2 rows; F2 generations were planted on 8 rows in the plots by hand into the holes made at 30 cm intervals. The plots were consisted of 8 m long rows with 70 cm inter spacing. All plots received 160 kg ha-1 nitrogen and 70 kg ha-1 phosphorus (P2O5) and a total of 11000 mm ha-1 of water through drip irrigation. First irrigation was done 45 days after planting. The field was hoed three times by hand and 4 times by tractor, and sprayed once against insects. Yield of seed-cotton (kg ha-1), yield of fiber (kg ha-1), height of plant (cm), duration of opening of first flower (day), node number of first fruiting branch, horizontal flowering Interval (day), vertical flowering interval (day), percentage of first picking (%), earliness index (day) and duration of mean maturity (day) were recorded and evaluated with respect to heterosis, heterobeltiosis, F2 deviation, F2 depression and correlations between the characteristics.

This summary report is based on a cross-cutting analysis of the present status of the cottonseed systems in nine African countries: three in West Africa (Benin, Cote d'Ivoire and Senegal), two in Central Africa (Cameroon and Chad), two in East Africa (Ethiopia and Tanzania), and two in Southern Africa (Mozambique and Zambia). Out of these nine countries, Benin, Cote d'Ivoire, Cameroon, Tanzania, and Ethiopia may be considered as major cotton producers in Africa (more than 50,000 metric tons of fibre produced each year). Together, they represent almost half of the African cotton production. The goal of this cross-cutting analysis is (i) to bring out the main characteristics of each cottonseed system studied, including the challenges to be addressed, (ii) to identify common and divergent features among these systems, and (iii) to draw lessons and propose recommendations for improving current cottonseed systems on a global scale in Africa. To do so, the full report describes and analyses the organisation of the cottonseed sector of each country, compares the situations between these countries, highlights the challenges encountered, and proposes actions to tackle some of the major challenges. This analysis considers four components of the seed system: (1) breeding and germplasm performance, (2) variety release, (3) seed production, and (4) seed management. For each component, a number of indicators cover the various activities and coordination mechanisms that have been put in place to guarantee the quality of the seed that reaches the farmers. Finally, the analysis proposes seven fields of action that can be adapted to the particular local situation and prioritized depending on their applicability, potential impact, resources available and urgency: - “Setting up an inclusive system for the cotton sector” is easy to implement: it mainly requires political and stakeholders' will; - “Providing quality seed”, “Selecting adapted seed areas”, and “Improving environmental sustainability” are rather easy to implement: the technical knowledge is available and the implementation of these measures doesn't require high levels of financial or political resources; training, and proper implementation is required; - “Giving value to quality seed” is more difficult to implement: it requires close interaction and real understanding among the actors, acute perception of the common interest, and significant resources; - “Fostering the breeding efforts” and “Training and capacity building” are based on significant investments, both human and financial, over longer periods of time; however they are essential and their cost and benefit can be mutualized by fostering efforts at a regional or even continental scale.

A mancha de ramularia, causada pelo fungo Ramularia areola e uma doenca foliar de ocorrencia generalizada no Cerrado Brasileiro comprometendo tanto a produtividade quanto a qualidade da fibra. O controle quimico e a principal estrategia adotada pelos produtores para evitar perdas economicas. Esforcos na busca de cultivares geneticamente resistentes tambem sao realizados e, nesse sentido, estudos sobre o controle genetico do carater e procedimentos experimentais adequados sao de grande importância. Esse trabalho teve por objetivo avaliar diferentes tamanhos amostrais de plantas de algodoeiro, visando uma otimizacao experimental na avaliacao da severidade da doenca. Para isso, um cruzamento biparental com genitores contrastantes para severidade da doenca, BRS 372 (resistente) e Coodetec 408 (susceptivel) foi utilizado, com cruzamentos, autofecundacao da geracao F1, e 189 plantas F2 conduzidas em condicoes controladas em casa de vegetacao e em cultivos subsequentes. As 189 progenies F2:3 foram conduzidas a campo na safra 2016/2017, em blocos aumentados de Federer, tendo por testemunhas as cultivares BRS 371 RF (resistente) e BRS 368 RF (susceptivel). Utilizou-se uma escala de notas de 1 a 5 para se mensurar a severidade da doenca, sendo o 1 correspondente a resposta fenotipica completamente resistente e o 5 a susceptibilidade completa. Aos 116 dias, 20 plantas em cada parcela foram avaliadas individualmente conforme a escala de notas. A partir de uma rotina desenvolvida no programa R foram simulados tamanhos amostrais considerando 1, 2, 4, 6, 8, 10, 12, 14, 16 e 18 plantas por parcela, realizando-se mil simulacoes para cada um deles, em que as plantas eram tomadas aletoriamente em cada parcela em cada simulacao, conforme o tamanho amostral desejado. O valor da severidade em cada parcela foi assumido como a media dos valores dos escores das plantas amostradas em cada simulacao. Os efeitos de blocos e progenies foram assumidos como aleatorios. Em cada simulacao foram obtidas estimativas dos seguintes parâmetros: media, variância genetica (VG), variância do erro (VE), variância de blocos, herdabilidade ao nivel de parcela (h2). Para cada tamanho amostral foram tomadas estatisticas descritivas das estimativas dos parâmetros considerando as mil simulacoes: media, mediana, desvio padrao, quantis 2,5% - q(2,5%) - e 97,5% - q(97,5%), esses dois ultimos como os limites bilaterais para 95% dos valores reamostrados. Em todos os tamanhos amostrais o escore medio das simulacoes foi de 2,2, com pouca variacao. Para a VG os valores medios tambem foram similares, variando de 0,30, com uma planta, a 0,34 para amostragens superiores a 12 plantas; contudo os q(2,5%) e q(97,5%) foram 0,17 e 0,44 com uma planta por amostra, e 0,33 e 0,35 para 18 plantas por parcela, indicando como esperado aumento na precisao da estimativa com o aumento do numero de plantas. A VE e a h2 foram os parâmetros mais afetados pelo tamanho amostral. A h2 de referencia, quando todas as plantas avaliadas foram consideradas na analise, foi 0,69 e 0,37 quando 1 planta foi amostrada; com 6 plantas amostradas foi de 0,62, com q(2,5%) e q(97,5%) iguais a 0,53 e 0,70. Os valores de q(97,5%) para a h2 foram identicos para tamanhos amostrais superiores a 6 plantas/parcela. Considerando-se todas as informacoes, recomenda-se o uso de pelo menos 6 planta/parcela para uma avaliacao segura da severidade de ramularia.

A absorcao de agua e nutrientes pelas plantas depende principalmente do sistema radicular. O deficit hidrico e o principal estresse abiotico que afeta o desempenho das culturas. Por ser conduzida principalmente em condicoes de sequeiro, a producao de algodao (Gossypium hirsutum L.) e muito dependente dos padroes de precipitacao pluviometrica. No Cerrado brasileiro, a presenca de veranicos e a ma distribuicao das chuvas impactam negativamente, tanto a fase vegetativa como a fase reprodutiva, reduzindo produtividade e qualidade da fibra.A arquitetura do sistema radicular (RSA) e composta por um conjunto de caracteres morfologicos, que compreendem o crescimento, a forma e a dispersao radicular no solo. O conhecimento da variabilidade genetica associada a caracteres de RSA em algodoeiro representa, portanto, estrategia crucial para o desenvolvimento de genotipos com sistemas radiculares que garantam, a planta, eficiencia na absorcao de agua e nutrientes, e tolerância a periodos de escassez hidrica. Este estudo integra informacao fenotipica e genotipica para compreensao das bases geneticas desses caracteres em um painel de 270 genotipos elite de algodoeiro, oriundo de 32 paises. O sistema radicular das plantas foi caracterizado por meio de plataforma de fenotipagem radicular, baseada em rhizotrons e tecnologia de processamento de imagens, identificada como PhenoRoots. As abordagens de modelo misto (REML/BLUP) e analise multivariada foram adotadas para o tratamento dos dados fenotipicos. Baseado nas informacoes do chip high-density CottonSNP63K Array, contendo 63 mil marcadores moleculares SNP (single nucleotide polymorphism), estudo de associacao genomica ampla (GWAS) tambem foi conduzido utilizando modelos single locus e multi locus. Os genotipos exibiram variacao significativa (pA e B2. Os outros dois mostraram-se associados com area total explorada pelas raizes e area explorada na profundidade 40-75 cm. A combinacao destes marcadores (i11178Gh e i06890Gh) resulta em quatro genotipos (AA, AG, GA e GG), em que 63% dos individuos com genotipo AA possuem morfotipo radicular do tipo A, correspondente a raizes profundas e com ampla area de exploracao; enquanto 76% dos individuos com genotipos GG possuem padroes radiculares superficiais (B1, C1 e C2). As potencialidades dos supostos ideotipos ainda carecem de validacao em campo. Tambem e prudente validar, em populacoes bi parentais, a associacao entre marcadores SNP e os caracteres de RSA. De qualquer modo, tanto os ideotipos como os SNPs aqui identificados em associacao com caracteres radiculares de interesse representam inovacao cientifica potencial para uso em programas de melhoramento do algodoeiro, visando melhor adaptacao da cultura a ambientes marginais.

: The root system architecture (RSA) of plants and its functioning play a fundamental role in a number of plant growth mechanisms including water and nutrient uptake. Optimization of the RSA is important for stable and increased plant productivity under adverse conditions. De-spite its great importance, studying the RSA is notoriously laborious because of the difficulty of accessing the rooting system of plants. We developed a root phenotyping platform, PhenoRoots, which allows for the non-invasive study of plant RSA. The system was built using inexpensive material and was designed to provide medium throughput. Substrate or soil-filled rhizotrons are used to grow plantlets, whose roots are directly visible through a glass plate. An experiment conducted on a panel of twenty Upland cotton ( Gossypium hirsutum L.) varieties demonstrated the usefulness of the platform in assessing RSA traits. A number of traits, destructive and non-destructive, related to the RSA were measured and statistically analyzed. The non-destructive traits based on image analysis of roots were more accurate and showed high correlation with the time-consuming destructive measurements. The platform allowed for capturing the phenotypic and genetic variability found in the panel of cotton varieties, and to define three contrasting RSA patterns. PhenoRoots provides an inexpensive alternative to the medium throughput analysis of RSA traits in plants.

En Afrique, en 2017/2018, 28 pays ont cultive du coton sur pres de 4,5 millions d'hectares, representant trois millions de petites exploitations, et ont produit environ 1,8 million de tonnes de fibre. Cette production, faible a l'echelle mondiale ( 87%) sous forme brute non transformee. Malgre un fort potentiel, la production a fortement chute au debut des annees 2000 et peine a s'accroitre. Les contraintes majeures identifiees sont les faibles rendements, le manque de financement des intrants, l'insuffisance des services de recherche et de vulgarisation, ainsi que la mauvaise qualite de la semence. Un programme d'amelioration de la semence de coton, finance par l'Agence de Cooperation allemande (GIZ) et porte par Cotton expert House Africa (CHA), a donc ete mis en oeuvre en 2018/2019 par le Centre de cooperation internationale en recherche agronomique pour le developpement (Cirad). Ce programme a porte en parallele sur les filieres cotonnieres de Cote d'Ivoire, de Tanzanie et de Zambie. Au cours d'une premiere phase, une etude sectorielle sur la semence de coton a ete effectuee. La deuxieme phase visera a partager les resultats de l'etude avec les acteurs locaux et a elaborer un plan de travail. Les premiers elements de l'etude sectorielle en Zambie et en Tanzanie ont ete presentes. Des recommandations preliminaires, portant sur l'organisation generale de ces filieres, sur la multiplication des semences et sur la creation varietale ont ete faites. Les prochaines etapes porteront sur l'elaboration et le partage de plans de travail et leur validation durant des ateliers nationaux reunissant les acteurs de la filiere coton de chaque pays de l'etude.

Gossypium hirsutum is the main cotton cultivated species because of its agronomically and fiber qualities. These traits had undergone different processes of selection and genetic improvement. In order to contribute to the study of cotton domestication we present global transcriptome analyses of wild and modern cotton using RNA-seq. Approximately 2000 genes were differentially expressed between wild and domesticated accessions. We also found a different expression contribution of homeologous genes, contained in each cotton subgenomes (A/D). Functional enrichment analysis showed that cellular component morphogenesis and cell wall organization genes were significantly represented in domesticated than wild cotton. Several other transcripts differences may provide clues about genes and processes that have been selected during domestication and breeding of modern lines. (Texte integral)

Background Cotton germplasm resources contain beneficial alleles that can be exploited to develop germplasm adapted to emerging environmental and climate conditions. Accessions and lines have traditionally been characterized based on phenotypes, but phenotypic profiles are limited by the cost, time, and space required to make visual observations and measurements. With advances in molecular genetic methods, genotypic profiles are increasingly able to identify differences among accessions due to the larger number of genetic markers that can be measured. A combination of both methods would greatly enhance our ability to characterize germplasm resources. Recent efforts have culminated in the identification of sufficient SNP markers to establish high-throughput genotyping systems, such as the CottonSNP63K array, which enables a researcher to efficiently analyze large numbers of SNP markers and obtain highly repeatable results. In the current investigation, we have utilized the SNP array for analyzing genetic diversity primarily among cotton cultivars, making comparisons to SSR-based phylogenetic analyses, and identifying loci associated with seed nutritional traits. Results The SNP markers distinctly separated G. hirsutum from other Gossypium species and distinguished the wild from cultivated types of G. hirsutum . The markers also efficiently discerned differences among cultivars, which was the primary goal when designing the CottonSNP63K array. Population structure within the genus compared favorably with previous results obtained using SSR markers, and an association study identified loci linked to factors that affect cottonseed protein content. Conclusions Our results provide a large genome-wide variation data set for primarily cultivated cotton. Thousands of SNPs in representative cotton genotypes provide an opportunity to finely discriminate among cultivated cotton from around the world. The SNPs will be relevant as dense markers of genome variation for association mapping approaches aimed at correlating molecular polymorphisms with variation in phenotypic traits, as well as for molecular breeding approaches in cotton.

Cotton producers worldwide suffer with the losses caused by the presence of phytonematodes. The aim of the present study was to investigate the inheritance of resistance to Meloidogyne incognita race 3 in Gossypium hirsutum variety punctatum accession TX 25. Accessions of Gossypium sp. were obtained from the germplasm bank of Embrapa Cotton. Two experiments were performed in two consecutive years. In the first experiment, a susceptible parental line, FiberMax 966, a resistant parental line, TX 25, and their F-1, F-2 and backcross generations were tested. In the second experiment, parental lines FiberMax 966 and TX 25, their F2 generation, and genotypes M315 (resistant), LA887 and DeltaOpal (moderately resistant) were tested. In both experiments, plants were inoculated with 2000 eggs and J2 of M. incognita race 3. The gall index, egg mass index and reproduction factor were evaluated 120 days following inoculation. In the first experiment, plants from the F-1 and backcross generations were susceptible. Plants from the F-2 generation presented a 3:1 resistant-to-susceptible ratio in the two experiments, indicating oligogenic resistance.

List of Gossypium samples genotyped for SNP diversity analyses. The table includes information for seed source, improved/wild classification, assigned categories for improved breeding regions, assigned categories for wild race types, availability of SSR genotypes for SNP-SSR comparison, and values for seed oil, protein, and seed index for samples used in GWAS analysis. In addition, for each sample, the coordinates of the first two MDS dimensions are listed for Figs. 3 and 4a, b. Five samples are included here that were identified as outliers and not used in the SNP analysis. Siokra 104–90 was not a cultivar developed in Australia (I. Wilson, personal communication). It may be a mislabeling of Siokra 1–4/649 which is actually just Siokra 1–4. (XLSX 97 kb)

A mancha de ramularia, causada pelo fungo Ramularia areola, e a principal doenca foliar do algodoeiro que ocorre no Cerrado brasileiro, podendo ocasionar desfolha precoce das plantas e comprometer a produtividade e a qualidade da fibra, reduzindo o lucro do produtor. A tatica de manejo mais usada e o controle quimico, sendo utilizados principalmente fungicidas a base de estano-orgânicos, benzimidazois, triazois, estrobirulinas e carboxamidas. Atualmente, sao necessarias por volta de oito aplicacoes de fungicidas em cultivares suscetiveis. O controle mais eficiente da mancha de ramularia e obtido quando as aplicacoes de fungicidas sao realizadas logo apos o aparecimento dos primeiros sintomas da doenca. Apesar da disponibilidade de controle quimico para a mancha de ramularia, esforcos dos programas de melhoramento visando obtencao de cultivares resistentes tem sido dispendidos, fato que contribuiria para reducao dos custos de producao. Contudo, uma das dificuldades para esse objetivo deve-se ao controle genetico da resistencia, possivelmente de natureza quantitativa. Esse trabalho teve por objetivo estimar parâmetros geneticos em uma populacao segregante de algodoeiro, obtida de cruzamento entre genitores contrastantes quanto a resistencia a doenca. A partir de um cruzamento biparental entre as cultivares BRS 372 (resistente) e Coodetec 408 (suscetivel), conduzido em condicoes controladas, obteve-se a descendencia F1, que foi cultivada em telado protegido e autofecundada para obtencao de uma populacao F2. Obteve-se um total de 189 plantas F2, que foram cultivadas em cultivo protegido e novamente autofecundadas. As sementes de cada uma das 189 plantas F2 foram colhidas e as 189 progenies F2:3 obtidas de cada planta foram cultivadas em campo na safra 2016/2017. O delineamento experimental foi de blocos aumentados de Federer, tendo por tratamentos comuns nos blocos as cultivares BRS 371 RF e BRS 368 RF, testemunhas resistentes e suscetivel, respectivamente, alem dos dois genitores como tratamentos regulares. A severidade da doenca foi mensurada mediante escala de notas de 1 a 5, em que 1 corresponde ao fenotipo completamente resistente e 5 ao fenotipo mais suscetivel. Aos 116 dias apos semeadura 20 plantas em cada parcela foram avaliadas tomando-se como medida de severidade da progenie a media aritmetica dos escores das plantas obtidos em cada parcela. Os efeitos de progenies e blocos foram assumidos como aleatorios sob enfoque de modelos mistos sendo estimados parâmetros geneticos e blups de progenies. Pela analise de deviância a estimativa da variância genetica para severidade da doenca foi significativa, indicando variabilidade na populacao segregante para selecao de plantas resistentes. A variância genetica foi cerca de tres vezes superior ao erro do experimento e cerca de seis em relacao a variância de blocos. A herdabilidade no sentido amplo em nivel de progenie foi de 0,64, indicando que cerca de dois tercos da variância total observada e devido a causas geneticas. A distribuicao de frequencia dos blups das progenies foi ligeiramente assimetrica, com 47% das progenies com blups abaixo da media populacional e 53% acima dessa. Treze progenies obtiveram estimativas de blups mais desejaveis que o do genitor resistente, enquanto 56 tiveram escores de blups superiores ao do genitor suscetivel, indicando assim segregacao transgressiva. Tendo-se como fonte de resistencia a cultivar BRS 372 e com base nos resultados obtidos, conclui-se que e possivel realizar selecao de genotipos de algodoeiro com resistencia a mancha de ramularia em cerca de 6% de progenies F2:3.

The root-knot nematode (RKN) Meloidogyne incognita is a serious pest of cotton, causing direct damages and increasing the severity of other root diseases. Host plant resistance and the development of resistant varieties have the potential to efficiently contribute to RKN management in cotton. High levels of resistance has been identified in a breeding line (Auburn 623 RNR) derived from a cross between two moderately-resistant accessions, and this source of resistance has recently been used to develop highly-resistant adapted lines. Nevertheless, continuous exposition to the same source of resistance may lead to the selection of virulent RKN isolates, and the identification of new sources of resistance is important for a durable resistance. We have previously demonstrated that G. barbadense accession CIR1348 (Mota et al. 2013; Da Silva et al. 2014) shows the same high level of resistance as the Auburn 623 RNR source, and in this work we describe the mapping of QTLs associated to RKN resistance in this novel source of resistance. An interspecific F2 population of 174 plants, constructed from a cross between the resistant accession CIR1348 and the susceptible Upland cotton variety FiberMax 966, was genotyped using SSR markers and plant reaction to inoculation with M. incognita race 3 was evaluated under controlled conditions. RKN resistance was scored using the following criteria: galling index (GI), egg mass index (EMI), number of eggs per gram roots (E/GR) and reproduction factor (RF). A genetic map was constructed using a set of 271 microsatellite markers, and a total of 262 loci assembled into 29 linkage groups at LOD ≥4. The total length map was 4,294 cM with an average distance of 15.1 cM between adjacent loci. QTL mapping identified four chromosomal regions harboring significant QTLs for one or more of the scored traits. Two QTLs (for GI on c2 and for EMI, E/GR and RF on c9) had a positive contribution from the susceptible parent FM966. A major QTL, with a positive contribution of the resistant parent CIR1348 was identified on c11, in the interval flanked by SSR markers CIR316 and CIR069. This major QTL mainly influences nematode egg production, and acted in conjunction with minor QTLs to confer the high level of resistance in cotton accession CIR1348. This same interval has been identified as harboring a major RKN resistance locus in other sources of resistance, including in M-315 RNR (Gutierrez et al. 2010; Jenkins et al. 2012), and this region of c11 has been shown to be rich in disease resistance genes (Wang et al. 2015). Similarly to other sources, the resistance in accession CIR1348 fits a two-genes model, but in contrast to the M-315 RNR line, resistance in CIR1348 is partially recessive. CIR1348 constitutes a new source of RKN resistance loci, and the identification of markers associated to major QTLs will facilitate the introgression of resistance into desirable genetic backgrounds. (Texte integral)

Partial virus genome sequence with high nucleotide identity to Cotton leafroll dwarf virus (CLRDV) was identified from two cotton ( Gossypium hirsutum ) samples from Thailand displaying typical cotton leaf roll disease symptoms. We developed and validated a PCR assay for the detection of CLRDV isolates from Thailand and Brazil.

High-throughput genotyping arrays provide a standardized resource for plant breeding communities that are useful for a breadth of applications including high-density genetic mapping, genome-wide association studies (GWAS), genomic selection (GS), complex trait dissection, and studying patterns of genomic diversity among cultivars and wild accessions. We have developed the CottonSNP63K, an Illumina Infinium array containing assays for 45,104 putative intraspecific single nucleotide polymorphism (SNP) markers for use within the cultivated cotton species Gossypium hirsutum L. and 17,954 putative interspecific SNP markers for use with crosses of other cotton species with G. hirsutum. The SNPs on the array were developed from 13 different discovery sets that represent a diverse range of G. hirsutum germplasm and five other species: G. barbadense L., G. tomentosum Nuttal × Seemann, G. mustelinum Miers × Watt, G. armourianum Kearny, and G. longicalyx J.B. Hutchinson and Lee. The array was validated with 1,156 samples to generate cluster positions to facilitate automated analysis of 38,822 polymorphic markers. Two high-density genetic maps containing a total of 22,829 SNPs were generated for two F2 mapping populations, one intraspecific and one interspecific, and 3,533 SNP markers were co-occurring in both maps. The produced intraspecific genetic map is the first saturated map that associates into 26 linkage groups corresponding to the number of cotton chromosomes for a cross between two G. hirsutum lines. The linkage maps were shown to have high levels of collinearity to the JGI G. raimondii Ulbrich reference genome sequence. The CottonSNP63K array, cluster file and associated marker sequences constitute a major new resource for the global cotton research community.

The root-knot nematode Meloidogyne incognita is widely distributed and a major pathogen of cotton (Gossypium spp.) worldwide. The objectives of this study were to assess the genetic variability and aggressiveness of Brazilian populations of M. incognita in cotton. Five populations of M. incognita and one isolate of M. enterolobii (outgroup) were used in the molecular analysis. Our results showed that only 2.7 % of the RAPD and AFLP fragments were polymorphic. Despite the existence of two races (races 3 and 4) and two esterase phenotypes (I1 and I2), a low genetic variability among populations was observed, which might be due to the mitotic parthenogenetic mode of reproduction of this pathogen. The aggressiveness/virulence among populations towards different cotton genotypes was also studied. None of the populations was virulent to the resistant cotton genotypes M-315 RNR, TX-25, CIR1343, Wild Mexican Jack Jones and CIR1348 (reproduction factor <1). Two populations of M. incognita from the states of Mato Grosso do Sul and Parana (Umuarama) (races 4 and 3, respectively) were highly aggressive to the susceptible control FM966 and virulent to the accessions LA-887 and Clevewilt-6 that showed moderate resistance to other populations tested.

The SSR marker CIR246, which is linked to the B 12 gene that confers resistance to race 18 of Xanthomonas axonopodis pv. malvacearum (Xam) , was used to evaluate a series of cotton germplasms that were also tested for their response to inoculation with race 18 of Xam (S-295, Delta Opal, 101-102B, Guazuncho-2, Acala 44, Mebane B1, and Stoneville 2B-S9). The allele associated with resistance was amplified in genotypes that carry the B 12 gene (S-295 and Delta Opal) as well as in those that carry B 2 B 3 (101-102B) and B 9L B 10L (Guazuncho-2), indicating that the molecular marker is able to identify genotypes resistant to the Xam races up to race 18, with resistance genes other than B 12 .