Impacts of delayed field curing of rice in a humid tropical environment on subsequent seed germinability and vigour

Raphael Kwame Bam, Sershen, Boby Varghese and Norman W Pammenter

Impacts of delayed field curing of rice in a humid tropical environment on subsequent seed germinability and vigour

Raphael Kwame Bam, Sershen, Boby Varghese and Norman W Pammenter

University of KwaZulu-Natal, South Africa

: J Plant Physiol Pathol

Abstract

A common post-harvest practice among rice farmers in Ghana is to field cure harvested panicles in the open field for about five weeks before threshing. Consequentially, the seeds may develop fissures and cracks, enhance physiological deterioration of both embryo and endosperm then, and during storage, and create favorable environment for seed microflora activity, especially fungi. In this study, three upland rice genotypes, viz. Oryza sativa, O. glaberrima and an O. sativa x O. glaberrima interspecific hybrid, were grown in Ghana, harvested, and cured in the open (wet) and within containers (dry) in the field for five weeks with objective of comparing the impacts of wet and dry curing on subsequent seed germinability and vigour. The relationships between air temperature and relative humidity (p<0.001), and seed moisture content and seed equilibrium relative humidity (p<0.001) differed significantly between curing environments. However, within curing environments, relationships between seed moisture content and seed relative humidity were comparable among genotypes. 18 fungal species each were isolated from seed samples from wet and dry environments; these included soil borne fungal species such as Alternaria spp., Sclerotium rolfsii, Trichoderma spp and Verticillium spp. in the wet environment. Fungal colonies was significantly (p=0.027) higher in dry-cured seeds, with O. sativa and O. glaberrima being significantly (p<0.002) more susceptible to fungal infection. Seeds with cracks were more prevalent in wet-cured seeds. These observations may explain why delayed field curing resulted in germination and vigour loss across all genotypes investigated. These findings have implications for rice seed curing and subsequent storage.