Physiological, morphological and biochemical responses of sorghum varieties to progressive water stress and rehydration in Siaya And Baringo Counties, Kenya
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Date
2025-02
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Kenyatta University
Abstract
Sorghum bicolor (L.) is an important food crop worldwide after maize, wheat, rice and barley. In Kenya, it is grown on an estimated 184,654 ha supporting over 25% as food and 26% as livestock feed. Despite having rich diversity in Arid and Semiarid Lands (ASALs), its production has been below the optimum mainly because of the abiotic stresses, with drought being the major stress. Drought is an impediment to sorghum productivity because it leads to water stress in the plant lowering its productivity. Drought tolerance enhancement under arid environments is a process that involves a mechanism of maintaining plant water status in order to increase grain yield and quality. A study was conducted with the objective of evaluating critical growth and phenological stages of sorghum sensitive to progressive water stress and rehydration in Siaya and Baringo counties where: (1) A field survey to acquire sorghum accessions was conducted in Siaya and Baringo counties; (2) Field experiments conducted in Siaya and Baringo counties to evaluate sorghum accessions for drought tolerance and (3) Selected sorghum varieties evaluated for physiological and biochemical responses to progressive water stress and re-watering in a greenhouse at KALRO Mwea. The field experiments were Randomized Complete Block Design (RCBD) with 15 accessions, two moisture levels in three replications in Siaya and Baringo sites. A controlled greenhouse pot experiment was conducted at KALRO Mwea constituting five stress levels (well-watered; continuous stress, pre anthesis, anthesis and post anthesis), four varieties in three replicates in two soil types collected from Baringo and Siaya. Stress was induced after crop establishment and re-watering done after each stress episode. Growth and phenological data on proline, chlorophyll content, soil moisture, stomata conductance, yields and grain quality were collected appropriately. Survey data was analysed using Statistical Package for Social Scientists (SPSS V 25). Field data was analyzed using R software version 4.2. Treatment means were separated using Tukey Honestly significance difference (Tukey HSD) at 5%. Results indicated that farmers used local seed accessions (46.5%), preferred sorghum traits included drought tolerance, disease and pests resistance. Varieties response to re- watering after prolonged stress duration differed significantly. The grain weights, plant height, SPAD values, shoot dry weight and grain weight were highly significant in both Baringo and Siaya soil types. Results from the two sites indicated that there were significant differences on number of days to anthesis (IH and 50%H), total filled grains (TFGW), total grain weight (TGW), grain number panicle-1 (GPnW) and shoot dry weight (SDW) in varieties within sites at p<0. The results showed that stress for a short duration up to Vegetative stage followed by re-watering recorded significantly low proline and other amino acids accumulation under both Baringo and Siaya soil. Gadam and Nyagem varieties recorded higher yields under stress conditions in Siaya site (p<0.05). The Nyagem and Gadam varieties are recommended to farmers in ASALs for increased food security, income and better livelihoods. The physiological and biochemical properties were elevated in case of drought tolerant varieties and this can be used as rapid indicators for sorghum selection for growth in ASALs.
Description
A Thesis Submitted in Partial Fulfilment of the Requirements for the Award of Degree of Doctor of Philosophy (PhD) in Agronomy in the School of Agriculture and Environmental Sciences of Kenyatta University, February 2025
Supervisors:
Prof. Joseph Onyango Gweyi
Dr. Rose N Mayoli