Physiological responses of cacao (Theobroma cacao L.) to biostimulants and plant growth regulators under abiotic and biotic stress
2024
Valleser, V.C.
Abiotic and biotic stress are major contributing factors in the reduction of yield in cacao. One possible solution to this problem is the application of biostimulants and plant growth regulators (PGRs). This study aimed to determine the effects of foliar application of biostimulants (oligocarrageenan and oligochitosan) and PGRs (cytokinin and paclobutrazol) on the reproductive characters of cacao trees under water stress, and on the physiological responses of cacao trees, grown with and without shade crop, and demonstrate their effectiveness as crop protection measures for the control of cacao black pod rot (BPR) disease. Biostimulants and PGRs increased the leaf chlorophyll index of cacao under water stress and light stress. Under water stress, flowering intensity was increased by the oligochitosan treatment. Cherelle wilt incidence was reduced by paclobutrazol, while cytokinin enhanced pod retention. The seed fresh weight, production of full beans, dry bean weight, and yield per tree were all improved by the biostimulants and PGRs treatments. Under low irradiance as in the coconut-cacao intercropping system, pod retention was improved by the foliar spray of biostimulants and PGRs. Furthermore, heavier pod and seed weight was noted from oligocarrageenan and cytokinin treatments. Overall, the foliar spray of biostimulants and PGRs under low light condition resulted in better pod index for cacao under BPR-stress, oligocarrageenan, oligochitosan, and paclobutrazol improved some of the yield-related parameters measured but disease incidence was unaffected. However, under in vitro conditions, the biostimulants and paclobutrazol were also effective as a protectant against, and eradicant of BPR disease in cacao. Foliar sprays of biostimulants and PGRs can be recommended to improve cacao production under abiotic and biotic stress.
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