Effects of drought on yield and yield components were investigated during the spring season 2000-2001 by growing 14 Indian mustard genotypes under irrigated and rain-fed conditions at Bharatpur and Jobner. A disease and pest management schedule was followed when required. The drought susceptibility index (DSI) for seed yield and component characteristics was calculated to characterize the relative tolerance of genotypes. Plant height, primary branches, secondary branches per plant, 1000-seed weight and seed yield were reduced under rain-fed conditions. The top five genotypes at Bharatpur that showed tolerance to moisture stress for seed yield, as indicated by their lowest DSI, were, in descending order PSR-20, PRO-97024, JMMWR-941, IS-1787 and PCR-7, whereas at Jobner these were JMMWR-941, RC-1446, PSR-20, RH-819 and ÔVarunaÕ. Of these, PSR-20 and JMMWR-941 were among the top six at both locations. These genotypes also showed relatively low DSI for one or more characteristics, such as primary branches per plant, secondary branches per plant, harvest index and seed : husk ratio. Genotypes with the lowest DSI, particularly for seed yield at both locations, would serve as useful donors in the breeding programme for improving the drought tolerance of existing Indian mustard cultivars.Key words: Brassica juncea -drought -susceptibility index -seed yield -oil content Rapeseed-mustard crops in India account for about 21.6% and 23.2% of the total oilseed harvested area and production, respectively (Anonymous 2004). Indian mustard is predominantly grown on nearly 90% of the total harvested area, covering up to 7.0 m ha. Nearly 37% of the total rapeseedmustard area is rain-fed, where the crop is severely affected by drought, resulting in acute yield losses particularly in the drought-prone areas of Eastern and Western India which are populated largely by resource poor farmers with small land holdings. The effect of drought depends on the time of its occurrence, duration and intensity. Mustard genotypes with drought tolerance trait(s) yielded better than those without such trait(s) under water stress conditions (Singh et al. 1988). Therefore, investigating the effects of drought on yield and yield components in Indian mustard is very important for identifying drought-tolerant traits that can be incorporated into high-yielding varieties. This study is aimed at investigating the effects of drought on a wide range of genotypes of Indian mustard and identifying suitable selection criteria for drought tolerance. Materials and MethodsPlant material and experimental locations: Fourteen genotypes of Indian mustard, Brassica juncea L. (IS-1787, BE-3121, RC-53, PRO-97024, RC-1446, DIR-673, RC-5, EC-347852, JMMWR-941, PSR-20, ÔVarunaÕ, PCR-7, RN-393 and RH-819) were grown during the spring season (October-April) of 2000-2001 at two locations in Rajasthan (India), Bharatpur and Jobner, which are approximately 230 km apart.The rainfall during the cropping season, October-April, was 0.5 and 0.9 mm at both locations, respectively, as this...

A total of 101 Brassica napus ssp. oleifera accessions with seed differing in glucosinolate and erucic acid contents were screened for resistance to four isolates of Peronospora parasitica at the cotyledon stage. Two groups of accessions with different resistance factors were identified. Lines that were homogeneous for resistance were selected from seedling populations of accessions that exhibited a heterogeneous reaction to some isolates. The resistance of one group differs from that of cv, Cresor, the only oilseed rape cultivar reported to have an isolate‐specific gene for resistance to P. parasitica. The isolate specificity of the second group was identical to that of cv, Cresor, A comparison of the response of host accessions which expressed moderate to full susceptibility at the cotyledon stage, with no clear differential response to any of the four P. parasitica isolates, indicated that those with high glucosinolate and high erucic acid contents (12 accessions) were slightly but significantly less susceptible than those with high glucosinolate and low erucic acid (19 accessions), or low glucosinolate and low erucic acid contents (28 accessions). The mean differences between accessions with low erucic acid but differing in glucosinolate content were inconsistent. The last result was further confirmed by investigating the expression of resistance to three isolates of P. parasitica at three different seedling growth stages among 11 accessions of oilseed rape with seeds low in erucic acid but differing in glucosinolate content.

Components of disease reaction, including incubation period, pustule types, inoculum production and disease index (DI); and contents of protein, phenols, soluble sugars and reducing and non‐reducing sugars were investigated in cotyledonary and true leaves of six genotypes of Brassica juncea: Varuna, Kranti, EC‐399296, EC‐399299, EC‐399313 and EC‐399301, inoculated with Albugo candida. Cotyledonary leaves were examined 14 days after inoculation (d.a.i.), whereas true leaves were scored 14 and 21 d.a.i. Disease indices were assessed on a 0% (resistant) to 100% (susceptible) scale. DIs at the cotyledonary leaf stage in the above six genotypes were 67, 65, 32, 31, 31 and 38%, respectively, whereas at the true‐leaf stage they were 21, 28, 12, 17, 9 and 4%, respectively at 14 d.a.i., and 35, 45, 17, 19, 20 and 6%, respectively at 21 d.a.i. Protein contents were highest in the genotypes with the highest DIs, such as Varuna at the cotyledonary leaf stage and Kranti at the true‐leaf stage, and lowest in the genotypes with the lowest DIs, such as EC‐399299 at the cotyledonary stage and EC‐399301 at the true‐leaf stage. Total phenols, total sugars, reducing sugars and non‐reducing sugars were generally negatively correlated with DI, but were not always consistent, particularly when differences in DI were small. The results indicated that factors conditioning the response of host genotypes to A. candida may differ or operate in different ways at different growth stages.

The response of a wide range of Brassica juncea accessions to 14 isolates of Peronospora parasitica, 12 from India (IP00A, IP02, IP03, IP04, IP04A, IP05, IP05B, IP33 and IP33A were derived from B. juncea; IP09, IP14 and IP13A from B. rapa) and two from B. napus in the UK (R1 and P003), was screened. Sixteen differential host response groups to these isolates (classified as groups A-P) were identified. Groups ÔAÕ and ÔBÕ expressed the widest resistance profiles to these isolates. Group ÔAÕ was susceptible to isolates IP05 and IP05B, moderately resistant to isolate IP33 and resistant to all other isolates. Group ÔBÕ was susceptible to isolates IP03, IP04 and IP04A, and resistant to the other isolates. Putative homozygous lines resistant to all 14 isolates were selected from the F 4 progeny of crosses involving lines RESBJ-200 from group ÔAÕ (selection from cv. Kranti) and RESBJ-190 from group ÔBÕ (selection from cv. Krishna). Both selections were selfed and tested for uniformity of reactions to all isolates for three generations. The resistance of RESBJ-200 to isolates IP00A, IP04A and IP33A seems to be conditioned by single dominant genes. The resistance of RESBJ-190 to isolates IP00A, IP05B and IP33A was also conditioned by single dominant genes. The gene for resistance to IP00A and IP33A in RESBJ-200 seems to be independent of the genes for resistance to the same isolates in RESBJ-190. The new genes for differential resistance to P. parasitica will be of value in future studies of the genetics of the host-pathogen interaction and for breeding for disease resistance.

Thirty‐one Brassica juncea accessions were screened at the cotyledon stage for resistance to four isolates of Peronospora parasitica. Isolates R1 and P003 were derived from crops of oilseed rape (B. napus ssp. oleifera) in the UK and isolates IP01 and IP02 were derived from crops of mustard (B. juncea) in India. B. napus cv. Ariana, which was used as a susceptible control for isolates from B. napus, was resistant to isolates from B. juncea. All, B. juncea accessions were resistant to isolates from B. napus except one accession which expressed moderate resistance to isolate P003. Five groups of B. juncea accessions with differential resistance were identified. Lines homogeneous for resistance were selected from seedling populations of accessions that exhibited a heterogeneous reaction to isolates from B. juncea. The differential resistance identified in the B. juncea‐P. parasitica combination can be used as a foundation for future studies of the genetics of the host‐pathogen interaction and for breeding for disease resistance.