Effects of temperature and leaf water stress on growth and flowering of litchi(Litchi chinensisSonn.)

Abstract

SummaryHigh day temperatures in the shoot (constant 20°C or 30°C day/10°C night or 30°C day/25°C night compared with 15°C day/10°C night) and high root temperatures (constant 27.5°C compared with constant 12.5°C or 15°C day/10°C night) promoted vegetative growth and reduced or eliminated flowering in ‘Tai So’ litchi. Higher temperatures also promoted the production of leafy rather than leafless panicles. Leaf water potential in most treatments during the day ranged from –0.3 to –1.5 MPa with warm days, cool nights and cool roots generally increasing tree water stress. A combination of warm shoots (30°C day/25°C night) and cool roots (constant 12.5°C) induced lower leaf water potentials (–1.0 to –2.0 MPa) and totally suppressed growth. Terminal buds grew out as vegetative shoots within two weeks when leaf water potential was increased (–0.3 to –1.5 MPa) by increasing the root temperature to 25–30°C. Starch levels were generally low (<5.0%) in mature leaves and roots, except for flowering plants at 15°C day/10°C night sampled at panicle emergence (6.2–9.8%). Starch levels were high in twigs, branches and trunks in non-flushing trees, especially in flowering trees at 15°C day/10°C night sampled at panicle emergence (10.6–12.6%), flowering trees at 20°C day and night and 12.5°C root harvested at anthesis (11.8–12.5%), and vegetatively dormant trees at 30°C day/25°C night and 12.5°C root (10.0–13.7%). The concentration of some nutrients in the shoots was increased by cool shoot temperatures and warm root temperatures. The levels of all nutrients, however, fell within the same range, in the standard nutrient table for litchi. A moderate or severe cyclical leaf water stress (irrigation when pre-dawn leaf water potential fell to –1.0 or –2.0 MPa compared to –0.6 MPa) and a constant moderate leaf water stress (–1.0 MPa) reduced vegetative growth in litchi (cv. Kwai May Pink) grown at 30°C day/25°C night. Flushing was completely prevented when plants were held at a severe constant leaf water stress (–2.0 MPa). Terminal buds grew out as leafy shoots when water stress (10°C root temperature and pre-dawn leaf water potential below – 1.5 MPa) was relieved after seven weeks and the plants maintained at 30°C day/25°C night, but were floral when transferred to 15°C day/10°C night. This experiment suggests that day shoot temperatures and root temperatures interact to control the level of flowering in litchi. Water stress appears to act by synchronizing vegetative dormancy in the branches before exposure to low temperatures. Flowering was very weak when day shoot temperatures and root temperatures exceeded 20°C. Poor flowering at high temperatures was associated with low starch reserves, especially in the twigs, branches and trunk.