The floral visitors of silky oak, Grevillea robusta A. Cunn. ex R.Br., their foraging behaviour and their effects on fruit-set were studied at Malava, western Kenya. Grevillea robusta is a popular tree for farm plantings in the eastern and central African highlands. Yield of seed has been disappointingly low in some areas and a lack of appropriate pollinators has been suggested as a possible cause. Investigations involved the monitoring of visitors on active inflorescences, assessment of the rewards available to potential pollinators, and exclusion experiments to establish the effects of various visitors on fruit-set. The flowers are visited mainly by birds and insects. The likely pollinators of G. robusta are sunbirds (Nectarinia amethystina, N. cyanolaema, N. olivacea, N. superba and N. venusta) and white-eyes (Zosterops kikuyuensis and Z. senegalensis). Very little aggressive behaviour between birds was recorded. No nocturnal pollinators were observed. Nectar was the major floral reward for pollinators, but is likely depleted by ants and honey bees, the foraging behaviour of which confirmed them to be nectar-robbers. These insects hardly ever touched stigmas during their visits. Eighty-nine per cent of bird visits were in the morning (07.00-10.00 hours) when nectar volume was highest. Inflorescences bagged to exclude birds set no fruits, and unmanipulated flowers and flowers bagged with self-pollen set no fruits, indicating a self-incompatibility mechanism. Control cross-pollinated flowers displayed greatly increased fruit-set (25.1%) compared with natural open-pollination (0.9%). All these findings confirm the importance of cross-pollen transfer to flowers and the neces- sity of pollinators for fruit-set. Effective seed production requires activity of pollinators for self-pollen removal and cross-pollen deposition. Seed production stands for G. robusta should be established where flowering is prolific and bird pollinators are abundant.

The reproductive biology of Grevillea robusta growing under exotic conditions in Kenya and Australia is reported. The species showed both protandry and a self-incompatibility mechanism. The stigma was wet and papillate with a distinct groove in the middle. The anthers dehisced prior to anthesis, when the perianth opened. Stigmatic receptivity began id after anthesis, with the greatest pollen germination rates and longest pollen tubes obtained 2 d after anthesis. Nectar secretion commenced with pollen dehiscence and was abundant at anthesis. Most stigmatic grooves opened widely 1-2 d after anthesis and stigmas showed taller papillae and abundant secretion. Controlled pollinations gave a greater fruit set from cross-pollination (5.9 % in April and 17.5 % in July) than open-pollination (0.1 % in April and 3.3 % in July). No fruit set from self-pollination was obtained in April, and very few fruit set for geitonogamous (two out of 1622; 0.1 %) or for autogamous (one out of 2707 flowers; 0.04 %) pollination treatments in July. Following self-pollination, growth of pollen tubes was poorer than in other treatments, and was generally arrested in the upper style. Cross-pollinated flowers produced normal and straight pollen tubes, while self-pollen tubes had growth abnormalities. Most of the open-pollinated flowers were found without pollen or with only self-pollen on their stigmas indicating that the amount of cross-pollen reaching the stigma under open-pollination may be a factor limiting seed production. Flowers shed soon after the fertilization phase were those with ungerminated pollen or no pollen. Although a very low rate of selfing may occur, G. robusta presents a self-incompatibility system and allogamy is its primary breeding behaviour. (C) 2000 Annals of Botany Company.

Haploid megagametophytes from a full-sib cross of Pinus radiata were used to construct a genetic linkage map for radiata pine based on random amplified polymorphic DNA (RAPD) markers. The map, which was made from 222 markers, was used to carry out a QTL analysis of growth using measurements made on seedlings from which these megagametophytes were collected at an early germination stage. Trends in the expression of QTLs for stem diameter, volume and height were compared using measurements made at 5 months of age, and at 1, 2 and 3 years of age. None of the observed trends showed complete stability, i.e. none of the putative QTL positions detected at any one age was strongly expressed at all of the four stages of measurement. However, 45% of the trends showed partial stability, i.e. putative QTLs significant at one age were also detected at a subsequent age. Trends in QTL expression with age followed one of three patterns: (1) putative QTLs at some locations showed a gradual linear increase in influence from 5 months of age and were highest at 3 years of age; (2) QTLs detected at 5 months of age gradually became less significant with age; and (3) some putative QTLs showed a curvilinear increase in effect from 5 months of age, reaching their peak expression at 1 to 2 years, and sometimes were still detected at 3 years of age.

NESTUR (needle-to-stem unit rate) is a stem growth index of conifer seedlings that measures the efficiency of stemwood production per unit of needle growth, and is related to other seedling traits such as height, stem diameter, stem volume and needle volume. Quantitative trait loci (QTLs) affecting the expression of stem growth efficiency in radiata pine seedlings were investigated using a RAPD linkage map constructed from markers scored on haploid, megagametophytic DNA. Four putative QTLs were detected which accounted for 8.5–36.4% of the population variance. A search for evidence of epistasis, using both complete pairwise and conditional interactions, did not yield any statistically significant result. Over a 3-year period, seedlings with high-NESTUR marker alleles showed a superior growth performance of 17–40% for height, diameter and volume over those with low-NESTUR marker alleles.

Needle-to-stem unit rate (NESTUR) is a stem growth index of conifer seedlings that measures the efficiency of stemwood production per unit of foliage growth. The random amplified polymorphic DNA (RAPD) technique was applied to haploid DNA from the megagametophytes of a full-sib radiata pine cross to find markers linked to factors controlling the NESTUR trait. Using the bulked segregant analysis approach, 23 of 933 primers displayed putative linkage to factors controlling NESTUR. Based on the genotypic analysis of 174 individuals, two quantitative trait loci (QTLs) controlling NESTUR were identified at ANOVA P -levels of 0.01–0.001. The QTLs were identified by RAPD markers OPE-06 450 and OPA-10 1200 , which were linked to each other ( r =7%), and UBC-333 550 , which was not linked to the other two. Linkage to components of NESTUR (increments in stem diameter and stem volume) was demonstrated for UBC-333 550 , while the others were not linked to NESTUR components.

Variation in oil yields from plantations and natural stands of Melaleuca alternifolia (Maiden and Betche) Cheel indicates considerable potential for improving plantation production through breeding. Some populations of the more widely distributed species, M. linariifolia Sm., produce a similar leaf oil and may provide opportunities to expand the genetic base of plantations. Growth and oil traits were assessed for 60 half-sib families, representing three chemical forms of Melaleuca alternifolia, and 10 half-sib families of the terpinen-4-ol rich chemical form of M. linariifolia, in a provenance/progeny trial in northern New South Wales, Australia. Differences in oil composition and coppicing between the terpinen-4-ol rich forms of the two species were significant (P < 0.05), while differences in growth traits and leaf oil yield were not significant. The difference in oil composition between northern and southern populations of M. linariifolia was as great as differences between the two species, suggesting the two regions should be considered distinct races for breeding purposes.

SYNOPSIS The detail of the pollination process in trees of slash pine (Pinus elliottii Engelm. var. elliottii L.&D.) has been studied following applications of mixtures of Honduras Caribbean pine (Pinus caribaea Mor. var. hondurensis B. & G.) and slash pine pollen in controlled pollinations. The studies have provided guidelines for pollen application in the monoclonal orchards, established in Queensland to produce seed of the hybrid between slash and Caribbean pines. These new orchards contain a single clone of slash pine and the pollen of Caribbean pine is applied artificially during the flowering period. Variation occurred between slash pine clones in seed potential and in the number of pollen grains usually present inside the pollen chambers. Both features may affect a clone's capacity to produce hybrid seed. The stage of cone development determined the entry of the pollen of both species. Caribbean pine pollen had no difficulty entering the pollen chambers in competition with slash pollen provided it was applied when the cones were receptive. Application of pollen prior to cone receptivity provided no advantage and late arriving pollen could still enter the chambers provided the cones were receptive. Pollen generally entered the chambers in approximately the same proportion as they were present in the pollen cloud. The results indicate artificial application of pollen could be scheduled for every two or three days in the monoclonal orchards. With misting applications Caribbean pine pollen should constitute at least 50% of the pollen cloud to ensure adequate numbers of pollen grains of this species in the pollen chambers. The counts of pollen grains inside the pollen chambers were compared with reported counts for other species of Pinus. There were important differences. Consequently there could be inter-specific differences in the degree of competition between pollen grains. Our studies suggest there could be similar differences between clones. There may be other important inter-clonal and inter-specific differences in the pollination process within the genus Pinus.