Genetic diversity and breeding value of okra (abelmoschus esculentus (l.) Germplasm for tolerance to two okra viral diseases under low and high nitrogen conditions

Abstract

Okra is a significant multipurpose vegetable crop cultivated extensively across the world. However, the productivity of the crop is constrained by abiotic (low N) and biotic (okra mosaic and leaf curl diseases) stresses. The excessive dependence on inorganic chemicals to combat viral diseases and low-N is harmful to the environment and unsustainable. Breeding for varieties tolerant to okra mosaic diseases (OMD) and leaf curl diseases (OLCD) with high N-use efficiency is the most practical and long-term strategy for reducing the losses caused by viruses and low-N. An assessment of genetic diversity and breeding value of okra germplasm for tolerance to okra mosaic and leaf curl virus diseases under low and high-N was carried out to identify hybrids and genotypes tolerant to low-N and the two viral diseases. Hundred okra germplasm were sourced, characterized and screened from Ghana's diverse agro-climatic and production regions. Twelve superior genotypes were selected based on tolerance to biotic and abiotic stresses and yield performance. Thirty-six (36) hybrids were generated from the twelve (12) germplasms using the North Carolina Design II mating scheme (NCD II). The 36 single cross hybrids together with four checks and the 12 parental genotypes were evaluated under low nitrogen (30 kg/ha) and high nitrogen (100 kg/ha) at two different locations, viz., Jacobu and Akumadan, during the major and minor growing seasons of 2021. The results of the diversity studies indicated wide genetic variability among the 100 okra germplasm studied, and 27 out of the 100 collected germplasms were duplicates. The parental genotype (Tamale 2E) was identified as the best low-N tolerant genotype with immunity against OLCD, OMD, and Podagrica spp. infestation under low-N environments. Similarly, Hilhaho × Paapa and Tamale 2E × G1 hybrids were identified as high-yielding, low-N tolerant hybrids and best-specific combiners. Also, single cross hybrid Paapa × Mampong had immunity against OMD, while hybrid cross Asontemtiatia × Paapa was the most resistant hybrid against OLCD under low-N conditions. Moreover, the study concluded that the additive gene effect was more significant than non-additive gene effects for the studied traits. Furthermore, maternal (cytoplasmic) effects influenced the inheritance of fruit yield and most yield components.