Effect of different salinity levels on yield and yield components of spring canola cultivars (Brassica napus L.) and Indian mustard (B. juncea L.)

IntroductionSalinity is one of the most important abiotic stresses that makes large areas of arable lands substantially or partially unproductive (Ashraf and McNeilly, 2004) and generally causes slowed plant growth rate, smaller leaves, reduced plant height and economic yield (Steppuhn and Raney, 2005). Two oilseed amphidiploids Brassica species including canola (Brassica napusL.) and Indian mustard (B. junceaL.) are relatively salt tolerant amongst oilseed crops. This experiment was conducted to evaluate seed yield, oil yield and yield components of two spring canola cultivars (Hyola 401 & RGS003) and Indian mustard and to compare these genotypes under irrigation with different salinity levels.
Materials and MethodsThis experiment was conducted as factorial based on randomized complete block design (due to lack of uniformity of the light) with three replications in the Research Greenhouse of Agriculture Faculty, University of Birjand, in 2015. The first factor consisted of four salinity levels including 1.9 (Hoagland solution as control), 5, 10 and 15 dS/m (NaCl in Hoagland solution) and the second one was genotype consisting of two spring canola cultivars (Hyola401 and RGS003) and Indian mustard landrace. The medium was sand culture in pots with 8 plants per 0.123 m2square-sahped cross section pot. Pots were irrigated from planting to emergence stage with distilled water and thereafter with Hogland solution using gravity drip irrigation system. At four-leaf stage, by adding sodium chloride to Hoagland solution, salinity stress was gradually started and continued until the end of maturity. At the end of every two weeks, pots were leached to avoid excessive accumulation of salts. At physiological maturity for each genotye, two randomized selected plants were harvested from each pot to determine seed yield and yield components. Seed oil percentage was measured using Soxhlet extractor (AOAC, 1990) and oil yield was calculated with multiplication of seed oil percentage by seed yield. Seed protein percentage was determined by the Kjeldahl method (Licitra et al., 1996). Data analysis and statistical calculations were done using SPSS and EXCEL softwares. Mean comparisons were accomplished according to FLSD Test, at 5% probability level.
Results and DiscussionAnalysis of variance on data demonstrated that the main effect of salinity and genotype on protein percentage and interaction effects of salinity and genotype were not significant on biological yield, while on all other traits were significant at 1% probability level. Results showed that by rising irrigation salinity up to 15 dS/m, amongst all seed and oil yield components the greatest and lowest significant reduction percentage compared to the control, were observed with the number of fertile pods per plant and seed oil percentage , respectively. Mean comparison of evaluated traits illustrated that Hyola 401 had the lowest amount of number of pods per plant and fertile pods per plant and possesed the highest amount of traits including 1000- seed weight and seed oil percentage which were significantly different from those of RGS003 and Indian mustard. Indian mustard in response to different salinity levels, with significant difference in comparison to canola cultivars, showed the lowest amount of evaluated traits including seed number per pod, 1000- seed weight and biological yield. RGS003, with significant difference in comparison to other genotypes, had the highest biological yield. The lowest seed yield of all genotypes was observed with the highest salinity level with a reduction of 73.31, 55.15 and 67.61 percent relative to control, which were achieved with Hyola 401, RGS003 and Indian mustard, respectively. There were not significant differences in oil yield between genotypes in salinity level of 15 dS/m, whereas in other levels Hyola 401 indicated a significant advantage. Correlation analysis of different traits showed that the most effect of salinity on oil yield in canola cultivars and Indian mustard was related to seed yield (r= 0.97**), biological yield (r= 0.75**), 1000- seed weight (r= 0.76**), number of seeds per pod (r= 0.74**), oil percentage (r= 0.64**) and harvest index (r= 0.59**).
ConclusionAmong the applied salinity treatments, the salinity level of 15 dS/m had the greatest effect on reducing studied traits. Seed and oil yield of Hyola 401 in comparison to two other genotypes showed significant advantage in low levels of salinity. However increased salinity level, resulted in a downward turn in yield differences, so that, at 15 dS/m no significant differences were observed.