Fruit cracking has long been a topic of great concern for growers and researchers of litchi (Litchi chinensis Sonn.). To understand the molecular mechanisms underlying fruit cracking, high-throughput RNA sequencing (RNA-Seq) was first used for de novo assembly and characterization of the transcriptome of cracking pericarp of litchi. Comparative transcriptomic analyses were performed on non-cracking and cracking fruits. A total of approximately 26 million and 29 million high quality reads were obtained from the two groups of samples, and were assembled into 46,641 unigenes with an average length of 993 bp. These unigenes can be useful resources for future molecular studies of the pericarp in litchi. Furthermore, four genes (LcAQP, 1; LcPIP, 1; LcNIP, 1; LcSIP, 1) involved in water transport, five genes (LcKS, 2; LcGA2ox, 2; LcGID1, 1) involved in GA metabolism, 21 genes (LcCYP707A, 2; LcGT, 9; Lcβ-Glu, 6; LcPP2C, 2; LcABI1, 1; LcABI5, 1) involved in ABA metabolism, 13 genes (LcTPC, 1; Ca²⁺/H⁺ exchanger, 3; Ca²⁺-ATPase, 4; LcCDPK, 2; LcCBL, 3) involved in Ca transport and 24 genes (LcPG, 5; LcEG, 1; LcPE, 3; LcEXP, 5; Lcβ-Gal, 9; LcXET, 1) involved in cell wall metabolism were identified as genes that are differentially expressed in cracked fruits compared to non-cracked fruits. Our results open new doors to further understand the molecular mechanisms behind fruit cracking in litchi and other fruits, especially Sapindaceae plants.

Litchi ( Litchi chinensis Sonn.), an important fruit originating in China, has received increasing attention for improving breeding efficiency in recent years due to the growing adoption of hybridization. It is a monoecious plant and predominantly relies on cross-pollination for seed production. Thus, enhancing pollen quality is essential for fruit set, which is closely associated with the developmental stages of male flowers. In this study, anthers of the litchi cv. ‘D13’ at five late developmental stages (half-exposed stage, fully-exposed stage, filament-elongated stage, anthesis, and browning stage) were investigated using paraffin sectioning, staining, in vitro germination, and controlled pollination techniques. Cytological characteristics of pollen were evaluated using paraffin sectioning, while pollen viability was assessed by I ₂ -KI staining, and the germination rate was determined through in vitro culture on sucrose media. Furthermore, pollen collected from these five stages was used for controlled pollination of the male-sterile line ‘MS1’. The results indicated that pollen collected at the filament-elongated stage and anthesis exhibited higher viability and germination potential, which resulted in improved fruit set in the male-sterile line ‘MS1’. The study identified the filament-elongated stage and anthesis as optimal stages for pollen collection in litchi.