Response of quantitative and qualitative characteristics of sugar beet genotypes to different sowing and harvesting dates

In semi-arid regions e.g. Iran, water is the major limiting factor for the growth and yield of sugar beet. Development of cultivars with flexible growth period, dependent on the environmental condition, is one of the methods to reduce water usage for sugar beet cultivation. The present study was performed in Sugar Beet Research Station of Motahhari, Karaj, Iran as a split factorial based on a randomized complete blocks design with four replications in two years (2015-16). Main plots were devoted to sowing date (mid-April and late-June), and sub-plots to the factorial combinations of three harvest dates (12 October, 1 November, and 21 November) and six genotypes including promising hybrids (7112*261)*5RR-87-HF.33 and 261*276.P.77.SP.19 and commercial cultivars Pars, Jolgeh, Paya and IR7. Potential root yield (RY) and sugar yield (SY) was reduced by 3.5-3.8% per week owing to delay in sowing. The significance of sowing date × genotype interaction (P<0.05) highlights diverse response of various genotypes to the shortening of the growth period. Superior genotypes for delayed planting were identified based on the combination of two components of the least response to delayed sowing as well as achieving the highest yield under delayed sowing condition in terms of SY as Paya, IR7, and Pars. Although the direct effect of harvest date on RY, SY, and sugar content (SC) was not significant due to the significant interaction of year × harvest date, however in general, it increased RY, SY, and SC by 21, 38, and 1.72 %, respectively via delaying the harvest date from 12 October to 1 November 1 in 2015. Therefore, the harvest date of 1 November was the most suitable time for sugar beets harvest in Karaj region. Non-significant interaction between sowing and harvest date for various studied traits indicated that the impacts of delay in sowing cannot be offset by delay in harvest. Overall, results showed that by each single day advancement in sowing (between mid-April and late-June) RY and SY increased by 400 and 50 kg ha-1, respectively and for each day delay in harvest (between 12 October and 1 November) RY and SY were increased by 370 and 100 kg ha-1, respectively.