Determining the seeding interval between two parents in any hybrid combination at a given location is of prime importance for achieving perfect synchronization in a hybrid rice seed production plot. Fixed growth duration, commonly practiced in India, is a simple and easy method to adopt. But fluctuations in temperature and other weather conditions influence maturity. Leaf number, unlike growth duration of a rice variety, is reported to be relatively stable over seasons and years.
For more than a decade, farmers in the irrigated area of Karnataka harvested yields of up to 7 t ha-1. No new technologies could help them increase yield further. Therefore, the major objective of the hybrid rice research begun at Mandya was to identify a suitable hybrid that could yield at least 1 t more than the check varieties. This objective was fulfilled by the release in 1994 of Karnataka Rice Hybrid 1 (KRH1) and in 1996 of Karnataka Rice Hybrid 2 (KRH2). The hybrid KRH1 (IR58025A/ IR9761-19-1R) has a yield potential of 7.5-8.5 t ha -1 and matures in 125 d. In 150 on-farm irrigated trials conducted in farmers' fields in different districts, KRH1 had a yield advantage of 1.5 t ha -1 over the check varieties. This hybrid possesses field tolerance for major pests and diseases.
The population of the developing world is becoming more urban. Are poverty and undernutrition beginning to relocate to urban areas as well? We use survey data on poverty (from eight countries) and on child undernutrition (from 14 countries) to address this question. Using data from the past 15–20 years we find that in a majority of countries the absolute number of poor and undernourished individuals living in urban areas has increased, as has the share of overall poverty and undernourishment coming from urban areas. Given these trends and the current stock of knowledge as to the levels, determinants and solutions to urban poverty and undernutrition, we argue for more research on these issues.
We are developing a system for Plant regeneration from wild species of Oryza. In recent work, dehusked seeds were surface-sterilized with 0.1% (w/ v) HgCl 2 solution for 5 min and rinsed four times in sterile distilled water. Sterilized seeds were kept for germination on MS medium devoid of growth hormones in light (1600 lux) at 25oC. The endosperm and radicle were excised from 7-d-old seedlings, which were then inoculated on MS medium supplemented with 6.0 mg BAP L -1 . Multiple shoots or micropropagules developed at the base of shoots were used for callus initiation. Segments (0.5-1.0 cm long) cut from their white tissue were inoculated on LS medium containing 2.5 mg 2,4-DL -1 , 3%) sucrose, and pH was adjusted to 5.8. The cultures were kept in the light. Embryogenic calli from the primary cultures were subcultured on the same medium and then transferred to regeneration medium based on MS salts supplemented with 2.0 mg BAP L -1 and 0.5 mg NAAL -1 . All media were solidified with phytagel (0.2% Sigma) and growth hormones avoided. Rooted plantlets were transferred to pots.
There has been much concern about soil degradation worldwide in recent years, and China has always been of special concern because of severe wind and water erosion in many areas. This paper puts together a tim e-series data set on soil quality indicators (organic matter, total N, total P, total K, pH) in China since the 1930s based on data from national geological and soil surveys. These data are presented separately for eight main areas of China (e.g., Huang-Hai-Huai Plain, Sichuan Basin). The paper also examines the simultaneous effects of agricultural yields on soil quality, and soil quality on agricultural yields by estimating cross-section regressions using counties as the unit of observation. The author stresses that these data have many shortcomings, but nevertheless it is probably the best data set currently available.
Our study aimed to examine genetic variability, heritability, and correlation coefficients among different characters when rice varieties were grown under saline conditions. We estimated the genetic parameters of seven quantitative characters in 20 rice genotypes grown under saline conditions. The experiment was laid out in a randomized block design and replicated three times during 1995-96 on saline soils (4-5 dS m -1 ) at the Rice Research Station “Jucarito,” Granma Province, Cuba. Hills were spaced 20 x 10 cm, with a single seedling hill -1 . Observations were recorded on five randomly selected plants replication –1 . The mean, standard deviation, phenotypic coefficient of variation (PCV), genotypic coefficient of variation (GCV), broad-sense heritability (h 2 ), and genetic advance as a percentage of mean (GA%) were calculated for seven traits. Path coefficient analysis was used to partition the genotypic correlation coefficient into direct and indirect effects.
The Cauvery Delta zone accounts forabout 22.3% of the rice area and 25.3% of rice production in Tamil Nadu State. Rice is cultivated in three distinct seasons-kuruvai (Jun-Oct), followedby thaladi(Oct-Feb) in double-crop wetlands and samba (Sep-Jan) in single crop wetlands. Transplanting continues to be themajor method of crop establishment forrice in this area. It requires more labor, time, and efforts. The scarcity and high cost of farm labor invariably delay transplanting and often lead to the use of aged seedlings. Uncertain release ofwater from the Mettur dam aggravates the situation for seedling age and time of transplanting.
0ryza minuta Presl., a wild rice species known to be resistant to bacterial blight and blast and green and brown planthopper, is endemic to the Malesian floristic region, specifically in Thailand, the Philippines, Indonesia, and Papua New Guinea. While it has been widely used in breeding and other experimental studies, its ecology and population dynamics remain poorly understood. In 1980, Vaughan documented six populations of 0. minuta located along a stream in Barrio Balian, Pangil, Laguna. Seed samples from these populations were collected and later conserved at IRRI's International Rice Genebank.
Rice production in saline soils could be increased if salt-tolerant genotypes were developed, but progress toward combining superior tolerance with good yield potential is slow, largely because of the nonavailability of reliable and efficient selection criteria. Selecting directly for grain yield under saline conditions may be limited by the low heritability of observed variation and failure to distinguish between yield potential and capacity to cope with adverse stress factors.
In the irrigated rice ecosystem that uses high-yielding varieties (HYVs), yields have already started plateauing. In India, where it is not possible to put more area into rice cultivation, adopting hybrids with suitable management practices would certainly be an alternative for increasing rice productivity. A study conducted at the C Block Seed Farm of BCKV during the 1998 and 1999 wet seasons examined the performance of hybrids as well as HYVs with different seedling ages and seedling number hill -1 .
Monosomic alien addition lines (MAALs) of O. sativa carrying single chromosomes of O. punctata were developed (Yasui and Iwata 1991). In the progenies of these MAALs, we identified plants in which the extra chromosome was telocentric or acrocentric.
The two parents of a hybrid combination differ in their growth duration and therefore flower at different times even when sown on the same date. To produce hybrid seed successfully on a commercial scale, male and female parents planted side by side in a fixed row ratio should flower simultaneously, which is called synchronization. Synchronized flowering between two parental lines of different growth duration can be achieved by seeding them on different dates which is termed seeding interval (SI). The method of arriving at an SI using growth duration is simple to practice. In this method, the difference between parental lines in the number of days to initial heading or 50% flowering from seeding is used to determine SI.
Development agents cite harvest and post harvest constraints as major factors in the profitability of irrigated rice production in the Senegal River Valley.Existing systems are expensive, too time-consuming, or too labor-intensive during periods of peak labor demand. An IRRI technology exchange with WARDA has provided a potential solution.
The influence of planting geometry (2015, 15´ 15, and 20´ 10 cm) and N levels (90 and 150 kg ha -1 ) on the productivity of two rice hybrids (TNH1 and TNH2) was evaluated in comparison with Rasi and Jaya as standard checks during the 1992 wet season. Planting densities of 0.33-0.50 million hills ha -1 did not significantly influencethe productivity of the test hybrids and varieties. The yield response to N application was significant up to 150 kg N ha 1 .
We studied the genetics of Al toxicity tolerance using a full diallel set of crosses among seven parents with differing degrees of response to Al toxicity. The seven varieties were Moroberekan, IRAT104, and Azucena (tolerant); IR29 and IR43 (moderately tolerant); and IR45 and IR1552 (susceptible). Relative root length of 14-d-old seedlings, determined by growing seedlings in a normal nutrient solution and nutrient solution with 30 ppm Al, was used to characterize the tolerance of test materials. The experiment was conducted in a glasshouse at the IRRI Phytotron with 29/21 oC day/night temperature and 70% relative humidity. The experimental units consisted of 49 entries (7 × 7 diallel) in randomized complete block design with four replications. Eight seedlings were sampled for each entry in a replication.
In this study, 15 plants per plot per line were selected to study the extent of damage caused by nine different insects of three orders (Hemiptera, Homoptera, and Orthoptera) belonging to five different families. These insect species were first identified in the experimental field and the damage they caused was characterized. The number of leaves damaged by any of these insects per plant was counted and expressed as a percentage of total leaves. Data were processed by analysis of variance, followed by Duncan’s multiple range test.
Bacterial leaf blight (BB) disease caused by Xanthomonas oryzae pv. oryzae (Xoo) limits rice yield in all major rice-growing regions of the world. As the bacterial pathogen is difficult to manage, the development of host-plant resistance is considered the most effective and economical means to control BB. Twenty-four major genes conferring resistance to various races of the pathogen have been identified and used in rice breeding programs (Lee et al 2001). Several varieties with high or moderate resistance to BB have been released under the auspices of the All India Coordinated Rice Improvement Project (AICRIP). Variety Ajaya (IET8585), released in 1994 under AICRIP, is highly resistant to all pathotypes in India (DRR 1996).
Boro rice cultivation is a special system of rice cultivation in low productive, waterlogged, low-lying deepwater land during November-May in eastern India. In such land, neither kharif (Jul-Oct) rice nor rabi (Nov-Apr) wheat is successful because of excess water. The boro crop is usually sown in November and transplanted when the temperature starts rising from January onward. The average minimum temperature during this period varies from 8 to 12°C. Crop productivity is very high (Thakur and Mishra 1990); consequently, boro rice has become popular in Bihar and eastern Uttar Pradesh. The suitability of rice varieties for boro cultivation mainly depends on their germination, tolerance for low temperature at the seedling stage, and seedling vigor.
