Pg. 9-14 The Physiology of Growth and Cropping in Lychee

Lychee or litchi (Litchi chinensis Sann.) is the most popular member of the Sapindaceae family that includes the related Jongan and rambutan. Lychee originated m the area near southern China and northern Vietnam, but has now spread to many countries: The largest producers are in South-East Asia (China, Vietnam, Thatiand and lnd,a), but the fruit is also popular in Africa (South Africa and Madagascar), Indonesia, Australia, the USA, Mexico, Spain and Israel. Average
yields range from 1 to 15 t ha^-1. Cropping is best in subtropical climates or at elevation in the tropics. In contrast, plant growth is acceptable across a range of soil types, provided the topsoil is well drained and attention is paid to micronutrient supply There are at least 100 varieties, but cultivation is generally limited to fewer than ten in most production areas. Some industries, in fact, are based on a single cultivar. The physiology of lychee growth, flowering and cropping is described, including the impacts of weather on flower initiation, a critical period during the production cycle. Orchard management including watering, fertilising, girdling, growth regulators and pruning can also have a large impact on tree growth yield and profitability Possible areas for future research and development are indicated.

Summary:

• Lychee (Litchi chinensis Sonn.) is a popular fruit originating from southern China and northern Vietnam, now cultivated in many countries globally, with largest producers in South-East Asia and smaller industries in places like Australia, South Africa, and the USA.
• Optimal cropping occurs in warm subtropical climates or tropical areas at elevation; poor flowering and fruiting happen in hot, moist equatorial zones despite good vegetative growth.
• There are over 100 lychee cultivars, but commercial cultivation generally involves fewer than ten, often centered on a single cultivar per region. Key cultivars differ by country and have traits like flowering time, eating quality, and seed size.
• Lychee growth involves repeated flushes of leaves, flowers, and fruit on new shoots, with flowering promoted by cooler winter temperatures below 20°C, particularly sustained low night temperatures around 15°C.
• Flower initiation is a critical period influenced by weather; lychee requires a cool dormant phase. Temperatures above 20°C reduce flowering, while excess heat or drought can negatively affect yield and fruit size.
• Water management: Dry periods before and during flower initiation can enhance flowering, but irrigation after flowering is essential to avoid reduced fruit size and yield. Lychee trees tolerate some drought and can extract deep soil water.
• Nutrient management: Nitrogen plays a vital role in leaf growth, flowering, and yield, with recommended leaf nitrogen levels around 1.5%. Phosphorus and potassium have less clear impacts, with some evidence that annual applications may be excessive if soil reserves are adequate.
• Canopy management through pruning controls tree size, improves flowering synchronization, and reduces losses to pests by facilitating netting and harvest. Pruning timing varies by location and climate.
• Growth regulators like synthetic auxins and ethephon can induce flowering and improve fruit set but require cool conditions to be effective.
• Girdling (cincturing) manipulates growth cycles to favor flowering but long-term effects on tree health are unknown.
• Future research priorities include breeding new cultivars for disease resistance, yield improvement, and harvest period extension; optimizing planting density and tree shape; refining water and nutrient management; and exploring safe growth regulator applications.
• The article emphasizes integrated orchard management—climate, water, nutrition, pruning, and chemical treatments—to enhance lychee productivity and profitability. It also highlights regional differences and the need for site-specific strategies.