Seed treatment with growth regulators and crop productivity. I. 2,4-D as an inducer of salinity-tolerance in wheat (Triticum aestivum L.)

Experiments were conducted under laboratory and greenhouse conditions to st udy the effect of 2,4-D on rooting and salinity tolerance of wheat. Seeds o f one commercial wheat (Inqalab-91) and three salt-tolerant wheat lines (WL -41, WL-359, and WL-1073 developed through wide hybridization) were include d in the study. Preliminary and short-term experiments were conducted to de termine the level of 2,4-D (administered through seed soaking for 24.5 h. a t 25 degrees C in the dark) at which the maximum number of roots emerged. U nder hydroponic conditions, 2,4-D treatment of seeds caused an increase of 60 to 100% in the number of primary roots. The maximum increase in the numb er of roots was observed in one of the salt tolerant wheat lines (WL-41). T he roots appeared in bunches but showed stunted growth at higher levels of 2,4-D. Dry matter accumulation decreased markedly; the effect was more pron ounced in Inqalab-91 which is less tolerant to stress than other wheat line s. In all wheat types, allocation of dry matter to roots relative to shoot increased due to 2,4-D treatment. In soil, seeds treated with different levels of 2,4-D showed a germination delay of 1-3 days. Although the number of primary roots increased, 2,4-D tr eatment caused a decrease in total dry matter accumulation by plants grown for 40 days. In another experiment, conducted under greenhouse conditions, seed germination and growth of seedlings was significantly retarded in sali ne compared to that in non-saline (normal) soil. Initially, the pace of ger mination of treated seeds as well as seedling growth was slower in both soi ls, but after six weeks, the leaf area of seedlings raised from treated see ds was greater than those raised from untreated seeds. Towards maturity, pl ants arising from treated seeds developed wider and longer flag leaves lead ing to enhanced yield. Root biomass decreased in saline soil as compared to normal soil. However, 2,4-D treatment caused a substantial increase in roo t biomass in saline soil and the roots were harder in texture in wheats oth er than Inqalab-91. Seed treatment with 2,4-D led to a significant improvem ent in the number of productive tillers, yield of straw and grain, and grai n protein content of all wheats grown in saline soil. Plants grown in norma l soil did not show any marked effect of seed treatment on grain yield and other agronomic parameters. The four wheats showed substantial differences for different parameters but the salt tolerant wheat lines performed better compared to the commercial variety Inqalab-91.