A comparison of the costs of flowering in ‘Feizixiao’ and ‘Baitangying’ litchi

Abstract

In this study, we investigated panicle size, blooming pattern, pollen viability and fruit set as well as changes in starch and soluble sugars in shoots and leaves, and N, P, K and free amino acids in panicles and flowers during panicle growth and blooming in litchi (Litchi chinensis Sonn. cvs. ‘Feizixiao’ (‘FZX’) and ‘Baitangying’ (‘BTY’). This was done in order to understand the nutritional costs for flowering and its relation to fruit set. ‘FZX’ had significantly larger panicles than ‘BTY’ but similar final set (2.8 fruit vs 2.9 fruit per panicle, averaged over three seasons). The averaged fruit retention rate to harvest over three seasons was 18.5% in ‘FZX’ and 28.2% in ‘BTY’. ‘FZX’ also had lower pollen viability. During panicle growth and especially blooming, the concentrations of carbohydrates in the shoots and leaves declined in both cultivars, with a greater decline in ‘FZX’. As a result, ‘FZX’ had a fewer carbohydrate reserves available for fruit development than ‘BTY’. ‘FZX’ panicle had a higher concentration of N, which provided nutrition for a larger panicle bearing a larger quantity of flowers. Abscising male flowers continued to accumulate N, P and K, which were not remobilized or reused but lost with flower shed. Before blooming, concentrations of total free amino acids increased in both cultivars. The concentration of Arg was higher than the other amino acids, suggesting flowering had a high demand for this amino acid. ‘FZX’ panicles had higher concentrations of amino acids than ‘BTY’. These results suggest that the nutritional cost of flowering is higher in ‘FZX’ than in ‘BTY’. The lower fruit retention rate in ‘FZX’ is related to the excessive consumption of carbohydrate reserve by flowering, leaving little for fruit set. Therefore, both pollen limitation and resource limitation contributed to the poor fruit set in ‘FZX’.