Evaluation of Winter Wheat Germplasm of Diverse Genetic Background for Heat Tolerance in Central Asia.

Two studies were conducted in Karshi, Uzbekistan to identify heat tolerant wheat genotypes. The first study in three years (2013–2015) using 105 winter wheat genotypes of diverse genetic background. Late planting was undertaken to expose the crop to high temperatures during grain-filling, which reached up to 43°C. Heat tolerance was assessed through changes in morpho-physiological traits under normal and late planting. Arrays of genotypic variations were found for traits related to heat tolerance. The 10 genotypes classified tolerant showed lower reductions (4 to 10%) in grain yield compared to the 10 sensitive genotypes (37 to 55%). The late seeded crop matured in 171 days compared to 209 days for timely seeded crop. The rate of decrease in NDVI (normalized difference vegetation index, a measure of leaf greenness and chlorophyll content) was faster in late compared to timely seeded crop. This suggests association between higher ambient temperature and chlorophyll breakdown. Genotypes exhibiting lower reductions in grain yield had slower rate of NDVI decline compared to heat sensitive genotypes. Lower reductions in grain yield were associated heavier kernel, taller plant height, and slower rate of NDVI reduction. Several genotypes (‘Alvd//Aldan/Ias58/3/Col.No.3617/4/Zarrin77’, ‘Alamoot/3/Alvd//Aldan"s"/IAS58/4/Alamoot/Gaspard’, and ‘Elomon’), identified as heat tolerant could be further evaluated for identifying new varieties or utilized as improved parents.

The second experiment involved evaluation of 24 spring wheat genotypes from ICARDA which had been selected for heat tolerance outside Central Asia. Several genotypes planted in March, considered an extremely late planting time, matured between 80 and 90 days with grain yield ranging from 3.3 to 5.6 t ha^-1 on medium saline soils under >40°C temperatures grain-filling in Aral Sea region. These fast maturing genotypes are viewed as valuable wheat material to be cultivated in winter frost-prone environments of Central Asia and other regions.