Studies on endogenous hormonal changes during grain development in wheat genotypes

Pot culture experiment was conducted in the Rabi seasons of 2001 and 2002 in order to study the genotypic differences in grain growth rates and endogenous hormonal contents in the developing grains. The hexaploid new plant types and extant variety and other tetraploids are taken up for the study. The data on yield and yield components show that the tetraploids had higher ear number per plant but lesser number of seeds per ear and lower seed weight per ear. The most important yield component 1000-grain yield was also possessed by hexaploids. The mean plant height was found to be higher in hexaploids over tetraploids in general, and among them DL- 1266-1 and DL-1266-2 (new plant types) recorded higher plant height. Similarly, the ear length was also higher in these new plant types. But, the tiller number/plant and ear number/plant were significantly higher in tetraploids. The new plant types (hexaploids) possessed maximum grain growth rate at 5–15 DAA. DL-1266-2 recorded highest grain growth rate 0.093 g/g/day. The photosynthetic rate values show that the hexaploids possessed higher rate than tetraploids. At 7 and 15 DAA, in general, photosynthetic rate was more when compared to 25 DAA and 35 DAA. The results showed that the endogenous hormonal contents in grains during grain development had changed in sequence. At 7 DAA, gibberellic acid (GA3) content was at maximum and at 15 DAA (rapid growth phase), indole-acetic acid (IAA) reached maximum and at 25 DAA (dough stage), ABA was at the maximum. At the 35 DAA, ABA reached all time high and GA3 the least, IAA being intermediate. Among the genotypes, hexaploids recorded higher concentrations of endogenous hormones. The total chlorophyll content in flag leaves of hexaploids was higher than tetraploids. The mean total chlorophyll had increased slightly at 20 DAA when compared to 10 DAA and it decreased at 30 DAA. It appears that the high yielding hexaploids (DL-1266-1 & Dl- 1266-2) by the virtue of possessing more 1000-grain weight and leaf area along with endogenous hormones might be responsible for higher yield as compared to tetraploids. It appears that better photosynthetic rate and better mobilization of photosynthates during grain filling stage contributes for higher yield in hexaploids.