Optimizing Sugarcane Cultivar Choice and Time of Harvest for Frost-Prone Environments in South Africa

Frost in low-lying areas in the midlands region of South Africa limits sugarcane (Saccharum spp.) yields and information on breeding strategies, cultivar choice, and time of harvest in frost-prone environments is lacking. This study aimed to (i) evaluate the yield and ratooning ability of test cultivars compared with commercial standards, (ii) identify an optimal time of harvest to maximize sugar yields, (iii) investigate cultivar differences in post-frost yield deterioration, and (iv) gain insights into future multienvironment testing strategies for breeding purposes. Four cultivar trials established between 2004 and 2008 showed that test cultivars 'N36', 'N41', and 'N48' produced significantly (P < 0.05) higher tonnes estimated recoverable crystal yields (TERC) than commercial controls ('N16' and 'N21') across multiple ratoons. Pre- and post-frost TERC estimates identified the mid-May to mid-June period as an optimal harvest time to maximize TERC, irrespective of frost onset or severity. Genotype + genotype x environment (GGE) biplot analysis showed that frost sites on humic and sandy soils are necessary when developing a breeding strategy. Cultivars N36, N41, and N48 may be suitable check cultivars for use in breeding trials. Cultivar N36 exhibited faster rates of TERC deterioration following frosts and may need to be prioritized for harvesting as a result. The estimation of pre- and post-frost sugar yields through sequential sampling and determination of key sugar yield components like stalk population are recommended for sugarcane frost studies. These methods are shown to produce more commercially relevant information than conventional estimates of post-frost quality responses alone.