A contribution to the life-history ofLitchi chinensis sonn.

Litchi Breeding for Genetic Improvement

Abstract: Litchi chinensis Sonn. ranks (high) among the most important horticultural crops, belongs to the family Sapindaceae and widely grown in tropical and subtropical regions (Menzel 1985). The tree produces delicious top quality fruits that are in great demand for their wholesome taste, sweet aroma and attractive colour. They are mainly consumed as a fresh table fruit worldwide but in China, dried litchis, called litchi nuts with the taste of the raisin are quite popular. They are also preserved and canned in syrup or used as squash. In Florida, frozen fruits are consumed on a limited scale. China, India and Taiwan are the major producers of litchi whereas in the last 40 years substantial increase in production in South Africa, Australia, Thailand, Vietnam, USA and Israel has led litchis to become a significant commodity in the international trade, (Underhill et al. 1997). Major thrust of litchi research has been on prevention of physiological browning and retention of bright red colouration of litchi fruits in several countries. Exotic litchi fruits have received worldwide attention. Increase in popularity has necessitated litchi cultivation in a wide range of environmental conditions. In fact litchi is generally adapted to various soil types via alluvial sands, loams, heavy clay, organic soil and calcareous soil with 30% lime and rock files (Chapman 1984a). In China, the best litchi trees are prevalent in Gwanagdong province close to the rivers on alluvial sands with good drainage and access to the water table (Chapman 1984b). They are also grown in gravelly sandy loam to loam soils as well as in swampy areas. However, soil in Fijian province is very high in clay, poorly drained and acidic in reaction (Winks et al. 1983). In South Africa, trees are more vigorous in growth on acid soils rather than on neutral or alkaline soils (Marloth 1947). Under Indian conditions, litchi cultivation in Bihar state is common on calcareous soils containing more than 40% free calcium carbonate and trees flourish well in a moist subtropical climate and in deep loamy soil with high moisture content. However,

Microsporogenesis and microgametogenesis of Cardiospermum grandiflorum and Urvillea chacoensis (Sapindaceae, Paullinieae)

Abstract: Microsporogenesis and microgametogenesis of two species, Cardiospermum grandiflorum Sw. and Urvillea chacoensis Hunz. (Sapindaceae, Paullinieae), were studied using light and transmission electron microscopy. Both species are monoecious, with staminate and hermaphrodite, although functionally pistillate, flowers. A comparative pollen-development study of these two floral morphs is reported. For the present study, five stages of pollen ontogeny were identified. The development of the anther wall is of basic type. Its wall consists of epidermis, endothecium, two middle layers and a uninucleate secretory tapetum. The microspore tetrads are tetrahedral. The mature anther in staminate flowers presents the endothecium with well developed fibrillar thickenings, remains of tapetal cells, a single locule formed in the theca by dissolution of the septum before anther dehiscence and two-celled pollen grains when shed. In functionally pistillate flowers, the mature anthers present remnants of the middle layers, tapetal cells without signs of degradation, the theca with two locules and pollen grains uni- or bicellular, some of them with the cytoplasm collapsed. These anthers are not dehiscent. It can be concluded that male sterility is characterised by failure to produce functional pollen grains, an event that would be associated with the persistence of tapetal cells. Ultrastructural analysis clearly shows the difference in tapetal cells between the two flower morphs.