Carica papaya responses under cool subtropical growth conditions

Under subtropical conditions papaw growth is adversely affected by minimum daily temperatures below about 11 degreesC. Optimum growth and development occur during the hot summer months when 2.5 new leaves are produced per week. Fruit set decreases from mid-summer (16 per plant/month) to early winter. During the colder winter months, plants produce few new leaves and no fruits are set, although previously set fruits continue to grow slowly by cell enlargement. Cell division occurs pre-anthesis and for 2-3 months post-anthesis. The shape of the sigmoid growth curve varies according to both month of fruit set and clone. Leaf size and leaf life increase from early winter- to late summer-emerging leaves. Plant canopy surface area increases from +-1 m(2) in early spring to 9-12 m(2) in autumn. Net photosynthesis is at a maximum between 16 and 25 degreesC. Root growth decreases from a peak in late summer to zero in winter. Pollen production and viability are adversely affected by cold winter conditions, which lead to necrosis of pollen mother cells, while high and low temperatures (> 32 degreesC and < 10 degreesC) have a temporary adverse effect on pollen viability. Fruit set, development and maturity (after 6-11 months) is affected by prevailing temperatures, competition with earlier set fruit and clonal selection. Peak production occurs in late spring and early summer with the last fruits ripening during the out-of-season period (February to April). Significant correlations were found between seed and fruit weight. Petiole NPK levels vary over time and application level. Carbohydrate content varies seasonally with peaks in reducing sugars and starch in the leaves, stems and roots during winter, as plant development slows down. Fruit sugar content rises from spring to summer-maturing fruits.