Fruit scientific research in New China in the past 70 years:Litchi

Abstract: Litchi is a typical subtropical fruit tree. China has a long history of litchi cultivation,with planting area of 551 746 hm2 in 2018,82.7-fold times that of 70 years ago,and production of about 3 028 100 t,an increase of 175.4-fold times. The production season lasts for 5 months from late April to the end of September. Most of the litchi trees were planted from mid 1980 s. More than 400 accessions have been collected and conserved in the National Litchi Germplasm Pool at Guangzhou. Thirty-eight new varieties have been selected and registered,and some of them have been widely expanded via regional trial planting. Hundred thousands of seedlings from cross breeding have been achieved. In order to increase flowering and fruit set the technique of spiral girdling on trunks and large branches during late fall and early spring was created,which has been very helpful to early bearing of the young litchi trees. As the coming of the new centery,lots of critical research progresses in molecular identification of important characters,biology in shoot growth,flower induction and fruit-set,soil and plant nutrition,pests and disease management,post-harvest physiology,processing,and mechanization have been achieved. Specificly,the hypothesis of phasic changes in floral differentiation,and“the skin versus blader effect”in the arillate fruit development were proposed. The process of litchi flower differentiation is composed of four visible stages: hardening of autumnal shoots before the first cold front in the early winter,floral induction under low temperatures,floral evocation(emergence of floral primordia,that is,“white millet”) as temperatures ascending in the early spring,and floral development under mild temperatures. The relationship between arils and skin of lychee fruit was investigated,and then“skin growth before arils”of lychee fruit was expounded. Cell division in the peel was found to occur mainly before flowering,and the cell numbers determined the fruit size.Water and solutes fastly entering the fruit,when skins fully expanded,may cause fruit cracking. Stable flowering,good fruit-set and large fruit sizes are potentially achieved with application of the major key technologies. It has been made clear that a large amount of laccases in the peel,is a phenoloxase located in vacuoles,which catalyzed epicatechin-mediated anthocyanin degradation and caused browning of the litchi pericarp. Research progress in soil and plant nutrition,plant protection,post harvest physiology,processing and mechanization are also commented. Litchi has been one of the crops granted from the China Agriculture Research System(CARS) since 2008. The litchi CARS subsystem is composed of 29 research scientists and 120 group members,covering 55 counties and 165 technicians. Looking into the future,we should focus on the research of breeding strategy,technology innovation in high-quality,productive,and green and efficient production,more adoption of new technologies including big data and artificial intelligence in litchi crop.