The involvement of the seed coat in low temperature germination of melon seeds was examined in two accessions differing in their ability to germinate at 14°C: `Noy Yizre'el' (NY) (a cold-sensitive cultivar) and `Persia 202' (P-202) (a cold-tolerant breeding line). Submerging the whole seed, or covering the hilum with lanolin, strongly depressed germination of NY, but not of P-202. Accessions differed in germination response to decreasing O2 concentration, with NY showing higher sensitivity to hypoxia. Intercellular spaces in the outer layer of the seed-coat were evident in the more tolerant P-202, while in the sensitive NY this layer is completely sealed. Sensitivity to hypoxia was greater at 15°C than at 25°C and was greater in NY than in P-202. It is proposed that the seed-coat imposed dormancy at low temperature in NY is the combined result of more restricted oxygen diffusion through the seed coat and a greater embryo sensitivity to hypoxia, rather than imbibition impairment or a physical constraint.
Fruit development and abscission in `Mauritius' lychee (Litchi chinensis Sonn.) were studied over three consecutive seasons. Each season, two distinct abscission periods were observed. The first started at the end of full female bloom and continued for ≈ 4 weeks. Of the initial number of female flowers, 85 % to 90 % abscised during this period. The second period began after a lag period of≈ 1 week and lasted ≈ 2 weeks. About half of the remaining fruitlets abscised during this wave. AU of these fruitlets contained an embryo. The second wave coincided with a period of rapid embryo growth and endosperm loss. Tipimon (a commercial product containing the triethanolamine salt of the synthetic auxin 2,4,5-TP) consistently and significantly increased marketable fruit yield when applied between the two abscission periods. Chemical name used: 2,4,5 -trichlorophenoxy propionic acid (2,4,5 -TP).