The degree of sterility resulting in F l hybrids has been used by several workers while considering the relative affinity between the different varieties and sub-species within a species and that between different species . The authors contend that sterility cannot be used as a criterion and present spikelet sterility data in F l hybrids of inter-varietal, inter-subspecific and interspecific crosses in the cultivated rices to support this contention . They conclude that the evolution of the three sub-species (viz ., japonica, javanica and indica) may have taken place independent of each other from the various ecotypes of the putative species Oryza perennis through introgression although the possibility of the indica giving rise to japonica on the one hand and the javanica on the other cannot be altogether ruled out .

No abstract

No abstract

Despite the increasing popularity in American markets of the fruit of the illustrious lychee (Litchi chinensis Sonn.), unreliable flowering and yield has had serious impacts on lychee growers in southern Florida. Lychee flowering is normally induced by chilling temperatures. Unpredictable weather, high rainfall, and excessive nutrients cause unreliable flowering in southern Florida. Although growers have no control over the weather, they need to be able to manage the growth, vigor, and reproduction of trees through practices that optimize flowering. When excessively watered and fertilized, lychee trees grow vigorously with frequent vegetative flushes every 2 to 3 months. The lack of maturity of these late vegetative flushes prevents flower stimulation from mild temperatures in January and February, when flowering typically occurs on trees that have not experienced vegetative flushes in the late fall or early winter. Thus, by adopting nitrogen fertilizer management practice, growers should be able to induce abundant flowering even in mild winters. Our preliminary results demonstrated that timing and rates of applications of nitrogen fertilizer significantly affected concentrations of soil and leaf N. High nitrogen levels in the leaves induced more vegetative flushes and less flowering, and consequently less fruit yield.