Assessing drought tolerance in Brassica species by root characteristics and plant water relations

摘要

Thirty four accessions of Brassica juncea and twenty seven of B. napus were planted in drought micro plots (size 6 × 1 × 1.5 m) under un-irrigated conditions (only pre-sowing irrigation) for root characteristics, plant water relations, yield attributes and seed yield. All traits differed significantly within each species. Association among different trails showed that the two species adopted different mechanisms in response to water stress. In B. juncea, leaf relative water content (RWC) decreased with decreasing leaf water potential (WP) while in B. napus RWC followed osmotc potential, which indicate that the former species had greater osmotc adjustment than the latter. The argument is further suported by the facts that decrease in WP RWC and osmotic potential (OP) promoted root growth in B. juncea but not in B. napus. Higher root weight resulted into deeper root zone depth in both the species. On an average root zone depth was greater in B. juncea ( 118.2 cm) than in B. napus ( 111 cm). In B. juncea, increased root zone depth led to higher number of primary and secondary branches, pods per plant while in B. napus root zone depth was associated only with the number of pods per plant. Consequently, increased biomass and seed yield were recorded in B. juncea as biomass and seed yield were positively correlated with decreasing OP. No such association was found in B. napus. Accessions EC 552573, 552579, 552580, 552581, 552582, 552583 and Rohini of B. juncea showed OP lower than-1.5 MPa whereas in B. napus,accessions EC 552585, 552588, 552597, 552599, 552601, 552602, 552603, 552607, 552609 and Neelam showed OP lower than -1.5 MPa. But the accessions inB. juncea maintained higher RWC than in B. napus. It is interestng to note that seed size was reduced due to higher osmotic adjustment in both the species. Reduction in RWC due to water stress decreased primary branches but not the secondary branches in the two species. In conclusion, water deficit decreased WP and RWC in B juncea resulting into greater osmotic adjustment and higher root growth which helped the plants to explore greater soil volume for water resulting in better yield attributes and ultimately seed yield.