MORPHO-PHYSIOLOGICAL ANALYSIS OF DROUGHT AND HEAT TOLERANCE IN WHEAT

Abstract

The present investigation was done to study the eco-physiological basis of heat and drought tolerance of wheat. It was conducted in a split plot design with three replications. The treatment factors were A. Main plot treatment: Four growing conditions viz. i. Well water growing condition (Giving three irrigations), ii. Water limited drought condition (Giving one irrigation at 20 DAS for seedling establishment). iii. Normal growing condition (sowing novmber 30, 2014) iv. Late growing heat stress growing (sowing December 30, 2014), and B. Sub plot treatment: Two wheat varieties: BARI gom-28 and Kanchan. From the results it was found that the days required to different phenological stages were significantly varied between two wheat varieties at different growing conditions. The requirements of days were decreased for both the varieties to attaining different growth stages at stressed (heat and drought either combined or single) condition compared to stress free (normal sowing with well watered) condition. To attain crown root initiation, tillering, heading, anthesis, physiological maturity and harvesting maturity stages, the maximum number of days required for BARI Gom-28, where as the minimum number of days required for Kanchan at both in stressed and stress free condition. At stressed condition both the varieties showed higher canopy temperature depression (CTD) compared to stressed free condition. Under highly stressed (late sowing heat stress with drought) conditions BARI Gom-28 showed the highest canopy temperature depression (6.1 0C ), where as variety Kanchan had the lowest CTD (4.5 0C ) at stress free condition. The chlorophyll content was decreased by both the wheat varieties at stressed (both heat and drought) condition compared to stress free conditions. At stress free condition, BARI Gom-28 had the maximum flag leaf chlorophyll content (2.8 mg/g fresh weight) and the lowest chlorophyll content was found in Kanchan at late sowing with drought condition (1.4 mg/g fresh weight). The proline content of all wheat varieties were increased at all the stressed conditions compared to stress free condition. BARI Gom-28 gave the significantly highest amount of proline (2.30 µmole/g fresh weight) at late sowing heat stress with drought, where as variety Kanchan produced the lowest proline content (1.65 µmole/g fresh weight) at normal sowing well watered condition. The stressed conditions reduced the plant height, spike length, spike number, spike plant-1, floret sipkelet-1, grains sipkelet-1 and grains sipke-1 of both the varieties compared to stress free conditions. Under stress free condition (normal sowing with well watered condition) BARI Gom-28 attained significantly higher value of these characters compared to Kanchan. The floret sterility of both wheat varieties were increased in different magnitude at all the stressed conditions compared to stress free condition. BARI Gom-28 gave the significantly lowest floret sterility (20.0%) at stress free condition. Under highly stressed condition (late sowing heat stress with drought) variety Kanchan showed the highest floret sterility (33.33%) compared to BARI Gom-28. It was observed that the stressed conditions reduced the grain yield of both wheat varieties compared to stress free conditions. Under stress free condition BARI Gom28 attained significantly higher grain yield (4.2 t ha-1) compared to Kanchan (3.6 t ha-1). At highly stressed condition BARI Gom-28 also had the higher grain yield (2.6 t ha-1) than the Kanchan (2.0 t ha-1). However, considering all stress combination BARI Gom-28 attained the highest grain yield (4.2 t ha-1) at well watered normal sowing condition whereas, variety Kanchan showed the lowest plant yield (2.0 t ha-1) at heat stress drought condition. BARI Gom-28 showed the significantly highest biological yield (9.5 t ha-1) at stress free condition compared to other growing conditions. Whereas, Kanchan produced the lowest biological yield (5.5 t ha-1) at highly stressed condition .BARI Gom-28 attained the highest harvest index compared to Kanchan at all the growing conditions. Due to lower stress susceptibility BARI Gom-28 was regarded as stress (both heat and drought) tolerant (SSI<1) and Kanchan was considered as stress sensitive due to higher SSI value (SSI>1)