Altered development, quality and sink strength in asynchronous maturing fruits produced from the two-sequence female flowers inflorescence/cluster of ‘Yu Her Pau’ litchi

Abstract

‘Yu Her Pau’ is one of the most dominant litchi (Litchi chinensis Sonn.) cultivars grown in Taiwan and China. However, the extremely large inflorescences often result in the production of early- and late- flowering female flowers (“two-sequence inflorescence”), thereby leading to the production of late-maturing fruit within the same cluster. This asynchronous maturity, often being regarded as a nuisance by growers and the impact of this trait requires further clarity. To document the alteration of growth and characteristics of fruits that mature asynchronously inside a cluster, 10-year-old field grown plants were used in the present study. Four categories of fruit: early- or late-maturing fruit in the presence of single cluster; and early- or late-maturing fruit in the presence of two-sequence cluster on trees were selected. The fruit growth curves and patterns, liquid endosperm retention in the embryo sac, primary (apparent) sink strength quantity and harvested quality were analyzed. The accumulated heat unit from fruit set to maturity was estimated. Flowering dates were noted to be three weeks apart, whereas harvest dates were noted to be only one week apart between the early- and late-maturing fruit because of the two-week longer maturity period of the early-maturing fruit. All categories of fruit exhibited single sigmoid curve and have commercial value at harvest. Early-maturing fruit from the early-maturing two-sequence inflorescence were approximately 50% heavier and matured two weeks earlier than the late-maturing fruit and exhibited significantly higher quality. The larger fruit from the early-maturing two-sequence clusters was associated with smaller seeds, higher absolute and relative fruit growth rates, longer fruit development periods in response to lower air temperatures pertaining at that time, greater primary sink strength quantity, longer retention of liquid endosperm, and higher accumulated heat units that were amassed during the pulp growth stage. In the meantime, the earlier dissipating of liquid endosperm in late-maturing fruit and in early-maturing two-sequence fruit was associated with decreased seed size. Late-maturing fruit in two-sequence clusters increased the primary sink strength quantity of early-maturing fruit in the same cluster. The results from our research should prompt a re-assessment of the physiological significance of the second-sequence of female flowers in litchi cultivars with extremely large inflorescence.