The effect of wild radish (Raphanus raphanistrum L.) flower morphology on the diversity, abundance, plant-pollinator interactions, and foraging behaviour of floral visitors in Lesotho.

Abstract

Wild radish (Raphanus raphanistrum), a prevalent weed in Lesotho, is known for its varied flower morphology and reliance on insect pollination. This study explores the diversity, abundance, and foraging behavior of insect pollinators in two agroecological zones of Lesotho: Nyakosoba research station and the National University of Lesotho (NUL) farm. The study further investigated the influence of flower morphology on pollinator-mediated selection, pollen removal, pollen production and comparison of seven floral traits between white and yellow color morphs. The Shannon-Wiener Diversity Index was used to measure species diversity, while cross-tabulation and chi-square tests compared pollinator abundance and visitation patterns. Descriptive statistics and ANOVA analyzed visitation rate, visitation frequency, and stay time, associating these behaviors with pollen deposition using ANCOVA. Descriptive statistics and linear regression model assessed pollen production. ANOVA was used to compare pollen removal from short and long stamens. Mean differences and standard errors of yellow and white flower morphs were compared using independent sample t-test. A total of eighteen insect species visited wild radish at NUL farm, and twenty-four species were documented at Nyakosoba, with Hymenoptera and Diptera being the most represented orders. Apis mellifera (honeybee) and Eristalis tenax (a syrphid fly) were the most abundant and effective pollinators. Visitation frequencies and stay times varied, with Stizus sp. and Apis mellifera showing the highest visitation rates. Floral visitors' preferences for pollen or nectar were also recorded, with Apis mellifera being the highest pollen forager. Yellow flowers with dark veins were predominantly visited by Eristalis tenax and Apis mellifera. Long stamens produced more pollen grains (mean = 6110.56 ± 384.87) than short stamens (mean = 4768.00 ± 389.99). More pollen was removed from dimorphic stamens (mean = 1.39 ± 0.08)han from long stamens (1.25 ± 0.05) and short stamens (mean = 0.91 ± 0.02). Morphological comparisons revealed significant differences in pedicel length (p = 0.01), anther length (p = 0.03), and pistil length (p = 0.05) between white and yellow flowers, though other traits showed no significant differences. These findings highlight that wild radish exhibits significant variation in flower morphology, which influences pollinator behavior and efficiency. Apis mellifera and Eristalis tenax were the most effective pollinators. Yellow flowers and long stamens were particularly favored, because of higher pollen production resulting in higher pollen removal. Future research should focus on investigating the genetic basis of floral trait variations in wild radish, explore further the impact of environmental factors on plant-pollinator interactions and v development of strategies to enhance pollinator services in agricultural systems by promoting floral diversity