GENETIC ANALYSIS OF COTTON (Gossypium hirsutum L.) GENOTYPES FOR DROUGHT TOLERANCE

Abstract

Drought is a major constraint that adversly affect the cotton yield and its fibre quality. In order to ascertain drought tolerant genotypes of cotton, three experiments based on morphological, physiological, fibre quality, yield and yield components of cotton genotypes under drought condition were conducted at two different locations. The morphological and physiological study was performed at Sher-e-Bangla Agricultural University, Dhaka. The fibre quality and yield experiment was conducted in the farmers‟ field at Godagari, Rajshahi. The fibre quality tests were executed at Fibre testing laboratory, Dhaka and Cotton Research Farm, Sreepur, Gazipur of Cotton Development Board. The duration of the experiments was from April, 2017 to March, 2020. Fifty cotton genotypes and four different treatments for drought stress were outlined in CRD for morphological and physiologica experiment and RCBD for fibre quality and yield experiment with three replications. Significant genotypic variations were observed for all the characters studied in all three experiments. Among all genotypes CB-12 is the highest ranked genotype for number of reproductive branches at early flowering stage and BC413 is the highest ranked genotype for root length. Heritability values in broad sense were

relatively high for almost all

the characters except number of vegetative branches. There is significant positive correlation between the number of reproductive branches and shoot length, shoot root length ratio, root diameter and total biomass of root both at genotypic and phenotypic level. Path analysis also revealed positive direct effect of these four traits on number of reproductive branches indicating these traits would help in further selection progress. According to DRI values, among fifty genotypes, twenty could be included in tolerant group at early flowering stage of cotton. Diversity studies revealed, fifty cotton genotypes were grouped into 8 clusters. The genotypes with high shoot length and no. of reproductive branch was observed in cluster IV. High root diameter and no. of lateral root in drought stress remain together in a cluster VII. Based on relative selection index (RSI) and drought response index (DRI) Ra-16 and BC-442 could be selected as tolerant genotype to drought at early flowering stage. In physiological studies at early flowering stage, among all genotypes CB-14 is the highest ranked genotype for pollen viability followed by water retension capacity and water uptake capacity. SR-16 is the highest ranked genotype for proline content. BC-394 was also higher ranked genotype for proline content as well as for water saturation deficit and relative water content. High heritability coupled with high genetic advanced in percent of mean was recorded for water saturation deficit, water retention capasity, water uptake capacity, membrane stability index and proline content indicating additive gene action controlling these traits and selection based on these traits will be rewarding. Correlation coefficient revealed positive and significant correlation among pollen viability and total chlorophyll as well as nitrogen content. Path analysis also showed positive direct effect of chlorophyll and nitrogen content on pollen viability. Based on RSI and DRI, BC-512, Ra-3, BC-413, CB-14, BC-385 and BC-394 could be selected as drought tolerant genotypes based on physiological study at early flowering stage. Among twenty five selected genotypes from previous two experiments, BC-433 had the highest rank for seed cotton yield per hectare followed by JA-13/R, BC272, BC-510. The lowest days to first boll bursting rank was found in CB-8 followed by

Ra-16 and CB-10. The

highest rank for Ginning Out Turn (GOT) was found in BC-272 followed by CB-11 and BC-442. High heritability coupled with high genetic advance at percent of mean was found for the traits, no. of vegetative and fruiting brunches, no. of bolls per plant, seed cotton yield per hectare indicating additing gene action controlling these traits and selection would be effective. Significant positive correlation with yield was found for the characters plant height, days to first square initiation, days to first boll split, no. of fruiting branch, no. of bolls per plant, single boll weight and seed index. Path analysis revealed positive direct effect of plant height, no. of bolls per plant and single boll weight on yield. Based on RSI and DRI values BC-415 is best ranking genoype for yield followed by BC-433 and BC-442, CB-14, CB-8 and BC-394. Regarding quality traits, genotypes JA-13/R had the longest fibre length, reflectance degree and fibre strength followed by BC-385, BC-433, CB-14, Ra-4, Ra-16 and BC-442. RA-08/9 had the highest micronnaire followed by BC-385 and CB-13. Ra-16 had the highest fibre strength followed by JA-13/R, Ra-3. Uniformity index had significant positive correlation with fibre length both at genotypic and phenotypic level. Path analysis also showed positive direct effect of uniformity index on fibre length. Based on SRI and DRI value, BC-510 is the highest ranking genotype followed by Ra-4, BC-385, BC-433, BC-413 and BC-462. Five genotypes as BC-415, BC-433, BC-442 and CB-14 for highest yield and three genotypes as BC-510, Ra-4, BC-385, BC-433, BC-413 and BC-462 for best quality fibre could be recommended to the farmers‟ of northern region of Bangladesh. Based on days to first square initiation, days to first flower initiation, days to first boll split and days to first boll bursting, BC-462 required further trial for earliness under drought prone areas.