Maize (Zea mays L.) seed quality in response to simulated hail damage.
Maize (Zea mays L.) is the most important cereal grain crop produced in various environments throughout South Africa. Maize is vulnerable to hail damage because it can reduce crop yield or may result in complete yield and quality loss. The objective of this study was to investigate the effect of simulated hail damage on maize physiology, growth, yield and seed quality of three popular maize cultivars [SC701, Mac Medium Pearl (MMP) and Zama Star (ZS)] at two different bioresource groups of KwaZulu-Natal (Swayimane and Baynesfield).Laboratory assessments were conducted using a completely randomised design replicated four times to test the seed quality (viability and vigour) before sowing. The three cultivars were analysed using tetrazolium, standard germination and electrolyte conductivity tests. Thereafter, a randomised complete block design replicated three times was used for the field experiments with three stages of simulated hail damage [control, V7 (9 weeks after planting) and VT (13 weeks after planting)] at three plant densities [(High) ca 65 000, (Moderate) 46 000, and (Low) 28 000 plants ha-1]. Data collection included plant height, leaf number, PAR, LAI, stomatal conductance and chlorophyll content index. At harvest, ear prolificacy, cob mass, cob length, and seed mass were measured. After harvest, the maize cob was separated into two halves (Proximal and Distal) for seed position factor. Seed quality (viability and vigour) was then determined using a completely randomised design replicated four times for Tetrazolium (TZ) and standard germination (SG) tests. Vigour indices that were measured were germination vigour index, mean germination time, seedling length (shoot, root and total) and seedling mass (fresh and dry) as well as root to shoot ratio. Moreover, the seed nutritional content quality was determined for protein content.Based on seed qulity results, the cultivars that were planted differed significantly (P<0.05) with respect to seed moisture content, 1000 grain mass, germination rate, final germination, shoot length, seedling length, electrolyte conductivity, germination vigour index, mean germination time (days) and seedling root to shoot ratio. However, tetrazolium test, root length, seedling fresh and dry mass showed no significant differences (P>0.05) among cultivars. There was no agreement between seed viability and vigour tests. Results of viability tests showed that the superior maize cultivar was SC701 followed by ZS and MMP, respectively. In contrast, based on electrolyte conductivity test, MMP had superior seed vigour compared to ZS and SC701, respectively. Field trial results showed that plant height varied significantly (P<0.05) between cultivars, sites and plant densities. The interaction between plant density and either hail damage or cultivar was significant (P<0.05) for plant height. Leaf number varied significantly (P<0.05) with respect to cultivars and plant density as well as the interaction of cultivars by site. The same was true for LAI. There were significant (P<0.05) differences between plant densities, sites, and their interaction for PAR. There were also significant (P<0.05) effects of cultivar by hail, plant density and site on stomatal conductance. Moreover, ear prolificacy was significantly (P<0.05) affected by site. Maize cob length was significantly (P<0.05) affected by cultivars, sites and interaction between cultivars and sites. After harvest, seed quality results indicated that there were significant effects (P<0.05) of plant density, seed position and BRG based on SG test. Proximal seeds had high seed quality with Baynesfield being the superior environment. Seeds from high plant density had superior quality with the best cultivar being SC701. Occurrence of hail damage at V7 or no hail damage was advantageous as expressed by standard germination and germination vigour. The TZ test showed that seed from Swayimane and applying hail damage at VT were more viable. There was a significant (P<0.05) interaction between cultivars, hail damage and plant density on seed protein content. Plants that were not subjected to hail damage, at low plant density and cultivar SC701had high seed protein content. It can be concluded from this study that stress caused by hail damage can influence seed quality. Management decisions such as planting dates, cultivar selection and plant population are important in mitigating hail damage effects on maize physiology, growth and yield. In addition to these management practices, seed selection based on the position on the cob is also an important determinants of maize seed quality. The findings of this study can be used to mitigate effects of hail damage on plant physiology and seed quality. Farmers from hail prone areas can select cultivar SC701, high plant density when growing their maize crops and select seeds form proximal part of the cob to use for the subsequent season. Further research can still be conducted on hail damage and other climate change induced environmental conditions on more than just the physiological seed quality and seed protein content. More research questions may be answered on biochemical, genetical and physiological stress indicators and mechanisms.