We exploited the newly developed amplified fragment length polymorphism (AFLP) technique to study the polymorphism, distribution and inheritance of AFLP markers with a doubled haploid rice population derived from 'IR64'/'Azucena'. Using only 20 pairs of primer combinations, we detected 945 AFLP bands of which 208 were polymorphic. All 208 AFLP markers were mapped and distributed over all 12 chromosomes. When these were compared with RFLP markers already mapped in the population, we found the AFLP markers to be highly polymorphic in rice and to follow Mendelian segregation. As linkage map of rice can be generated rapidly with AFLP markers they will be very useful for marker-assisted backcrossing.

To lay the foundation for molecular breeding efforts, the first genetic linkage map of mulberry (2n=2x=28) was constructed with 50 F1 full-sib progeny using randomly amplified polymorphic DNA (RAPD), inter-simple sequence repeat (ISSR), and simple sequence repeat (SSR) markers and two-way pseudotestcross mapping strategy. We selected 100 RAPD, 42 ISSR, and 9 SSR primers that amplified 517 markers, of which 188 (36.36%) showed a test-cross configuration, corresponding to the heterozygous condition in one parent and null in the other. Two separate female and male maps were constructed using 94 each of female-and male-specific testcross markers, containing 12 female linkage groups and 14 male linkage groups. At a minimum logarithm of the odds (LOD) score threshold of 6.0 and at a maximum map distance of 20 cM, the female map covered a 1,196.6-cM distance, with an average distance of 15.75 cM and maximum map distance of 37.9 cM between two loci; the male-specific map covered a 1,351.7-cM distance, with an average distance of 18.78 cM and a maximum map distance between two loci is of 34.7 cM. The markers distributed randomly in all linkage groups without any clustering. All 12 linkage groups in the female-specific map consisted of 4-10 loci ranging in length from 0 to 140.4 cM, and in the malespecific map, the 13 largest linkage groups (except linkage group 12, which contained three loci) consisted of 4-12 loci, ranging in length from 53.9 to 145.9 cM and accounting for 97.22% of the total map distance. When mapping, progeny pass through their juvenile phase and assume their adult characters, mapping morphological markers and identification of quantitative trait loci for adaptive traits will be the primary target. In that sense, our map provides reference information for future molecular breeding work on Morus and its relatives.

Agricultural environments deteriorate due to excess nitrogen application. Breeding for low nitrogen responsive genotypes can reduce soil nitrogen input. Rice genotypes respond variably to soil available nitrogen. The present study attempted quantification of genotype x nitrogen level interaction and mapping of quantitative trait loci (QTLs) associated with nitrogen use efficiency (NUE) and other associated agronomic traits. Twelve parameters were observed across a set of 82 double haploid (DH) lines derived from IR64/Azucena. Three nitrogen regimes namely, native (0 kg/ha; no nitrogen applied), optimum (100 kg/ha) and high (200 kg/ha) replicated thrice were the environments. The parents and DH lines were significantly varying for all traits under different nitrogen regimes. All traits except plant height recorded significant genotype x environment interaction. Individual plant yield was positively correlated with nitrogen use efficiency and nitrogen uptake. Sixteen QTLs were detected by composite interval mapping. Eleven QTLs showed significant QTL x environment interactions. On chromosome 3, seven QTLs were detected associated with nitrogen use, plant yield and associated traits. A QTL region between markers RZ678, RZ574 and RZ284 was associated with nitrogen use and yield. This chromosomal region was enriched with expressed gene sequences of known key nitrogen assimilation genes.

these major genes (Gallagher et al., 1994;Ketipearachchi et al., 1998). It has long been suggested that quantita-The brown planthopper (BPH), Nilaparvata lugens (Stå l) (Homotive resistance should be more durable (Heinrichs, 1986; ptera: Delphacidae), is one of the major insect pests of rice (Oryza sativa L.). Many major genes are now available to manage this pest Bosque-Perez and Buddenhagen, 1992). Until recently, through host-plant resistance. In this study, we mapped quantitative the genetic basis of quantitative resistance to insect pests trait loci (QTLs) associated with resistance to BPH using a doubled could not be explained owing to the inherent complexity haploid (DH) population derived from the cross IR64/Azucena. We of the trait and the limitations of conventional genetic evaluated a set of 94 DH lines using a series of phenotypic tests that tools. With the advent of new molecular genetic tools, cover seedling resistance and resistance mechanisms: antixenosis, antithe search for genes involved in complex traits has bebiosis, and tolerance. QTL analysis detected six QTLs on chromosomes come a rapidly developing area of research. In the past 1, 2, 6, and 7 associated with resistance to BPH in this mapping populadecade, there has been great progress in identifying tion. The QTLs on chromosome 7 (Est9-RZ337B) and 2 (RG157chromosomal regions that influence quantitative resis-RZ318) showed their association with seedling resistance and antibiotance to insects in many plants (Yencho et al., 2000). sis, respectively. Four QTLs on chromosomes 1 (RG146-RG345), 6 (RG213-Est2; Pgi2-pRD10B), and 7 (RG773-Est2) showed their IR64, an indica variety adapted to irrigated conditions and Published in Crop Sci. 44:2214-2220(2004.

Cooking quality in rice grains is a complex trait which requires improvement. Earlier reports show varying genetic inXuence on these traits, except for a common agreement on waxy (Wx) and alkali degeneration (Alk) loci on chromosome 6. The present study involved 86 doubled haploid lines derived from an indica £ japonica cross involving IR64 and Azucena. Grain parameters viz., raw grain length (RGL), raw grain breadth (RGB), cooked grain length (CGL), cooked grain breadth (CGB), gelatinization temperature (GT), grain shape (RGS), length elongation ratio (LER) and breadth expansion ratio (BER) were subjected to mixed model mapping of quantitative trait loci (QTL). Segregation data of 175 markers covering a distance of 2395.5 cM spanning the entire genome were used. Fifteen main eVect QTLs were detected spread over the genome, except on chromosomes 4, 8 and 11. Thirty epistatic interactions signiWcantly inXuencing the traits were detected. Twelve of the main eVect QTLs were involved in epistatic interactions. One main eVect QTL associated with LER was detected near Alk locus. QTLs located for grain length on chromosomes 9 and 10 are reported for the Wrst time. Detection of many epistatic loci and involvement of main eVect QTLs in interactions demand for judicious selection of QTLs in markerassisted selection programmes.

Cassava mosaic disease (CMD) is the most serious disease in cassava-in India where it is grown for food, starch and sago purpose. The disease is best kept under control by exploiting the available host plant resistance, which was introgressed from M. glaziovii to cassava and it is known to be polygenic control. In the present study, an attempt was made to construct the genetic linkage map of cassava using SSR markers with the objective of mapping genes associated with CMD. Using single marker analysis (SMA), four CMD resistance markers were detected viz. SSRY28, SSRY235, SSRY44 and NS136. SSRY28 and SSRY235 were located on linkage group G and SSRY44 and NS136 on linkage group P of cassava genetic map developed by Fregene et al. (1997). Among the four markers, three (SSRY235, SSRY44 and NS136) are new markers associated with CMD resistance. The detection of markers SSRY44 and NS136 having association with CMD resistance is a new report indicating the possibility of having another genetic loci for CMD resistance in cassava in addition to the already established on linkage group G. This finding supports the polygenic control of CMD resistance.

In the present study a population consisting of 247 F 2 individuals from the cross between Basmati 370, a superior quality basmati variety and ASD16, a non-basmati high-yielding variety was analyzed for their segregation pattern of grain length (GL), grain breadth (GB), cooked grain length (CGL), cooked grain breadth (CGB), and gelatinization temperature (GT). Except GT, all other traits showed normal distribution indicating the polygenic control over the traits. The correlation analysis between traits indicated that GT had positive significant association with GL (0.125), and CGL (0.243). To identify main effect QTL (MQTL) for the above grain quality traits, both the parents were surveyed with 86 primer pairs of simple sequence repeats (SSR). The parental survey revealed 63.95% polymorphism between parents. In order to detect the MQTL associated with grain quality traits, a strategy of combining the DNA pooling from selected segregants and genotyping was adopted. The number of individuals forming the bulk influenced the identification of putative marker(s) for each of the traits. The association of putative markers identified based on DNA pooling from selected segregants was established by Single Marker Analysis (SMA). The results of SMA revealed that SSR markers, RM225 on chromosome #6 and RM247 on chromosome #12 showed significant association with GB and CGB respectively. It is established that molecular marker analysis involving DNA pooling of phenotypic extremes and selective genotyping helps to detect MQTL for complex traits involving early segregating generations. The molecular marker analysis involving the DNA pooling of phenotypic extremes could be a useful strategy to detect the genetic loci with major effects of other complex grain quality traits in rice.

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