The effect on Citrus fruit of excluding pollinating insects at flowering and implications for breeding new seedless cultivars

Abstract

SummaryExperiments were conducted with orchard and container-grown trees of 33 Citrus cultivars in which pollinator insects were prevented from visiting flowers. Seventeen cultivars set fruit under orchard conditions when insects were excluded from flowers by mesh bags, while 16 others failed to develop fruit. Of the cultivars that set fruit in bagged limbs, four gave seedless and 13 gave seeded fruit. In addition, two pollen-sterile hybrids of ‘Imperial’ mandarin ‘Hamlin’ sweet orange set seedless fruit when insects were excluded at flowering, but developed seeded fruit in open-pollinated situations, or when controlled cross-pollinations were made. One of these hybrids was used to demonstrate that wind was not a pollen vector. Glasshouse experiments confirmed the results obtained for some of the cultivars tested in the orchard. Variation in anther position relative to the stigma among five cultivars suggested that self- or auto-pollination can occur without vector intervention. ‘Ellendale’ tangor, as well as ‘Imperial’ and ‘Kara’ mandarins were shown to be capable of autonomic, parthenocarpic fruit development. The results are discussed in terms of screening for parthenocarpy when breeding new seedless Citrus cultivars.