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Experiments were conducted to test the effect of vapour pressure deficit and temperature at time of spraying on the ethephon-accelerated ripening response in tomatoes. Neither factor influenced ripening rate or the rate of leaf senescence. The results of these experiments suggest that the response to ethephon is not affected by the rate at which the solution dries on the leaf or on temperature per se, at application rates that are normally used on tomatoes.

The titne during which pollen development is most sensitive to chilling was investigated. Five cultivars of totnato {Lyeopersieon esculentum Mill,) bearing flower buds at diffetent stages of developtnent were kept at 7"C for 1 week under 12-h light periods, during which titne growth stopped. After returning the plants to tninimutn tetnperatures of 18 "C, the presence of chrotnatin in the pollen was assessed daily as the flowers reached anthesis. The results suggested that there are two stages of acute sensitivity to cold during pollen developtnent, each of which tesults in cold-sttessed plants having pollen empty of chtomatin. The first and tnost sensitive stage is about Il,2d (SE = 0,3 d) before anthesis, and this is followed by a second stage of sensitivity about 5,6 +0,2 d before anthesis. Flowers that had wholly developed under sitnulated natural tetnperatures that decreased diurtially frotn a tnaxitnutn of 18°C to a tninitnutn of 7 C also had defective pollen, but pollen of nortnal appearance was regained within 14 d on teturn to higher tetnpetatures. Plants of L. esetilenttmu and a fortn (LA 1363) of the wild species L. hir.siitum frotn high altitudes in the Andes, as well as Fl and F3 generations of their hybrid, were grown to the floweritig stage at an altitude of 600 tn in Hawaii and then grown for a further 30 d at 2000 tn, where night tetnperature was below 10°C, The high altitude environtnent severely affected the quality of pollen produced and its release from the statnen in L. escutentum, but not in L. hirstittim LA 1363, The results with the hybrids suggested that such tropical mountain environtnents can be used as a 'natural phytotron' in the selection of chilling resistance that is only expressed in the mature plant,

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