Relationship Between the Capacity to Ripen and Ontogeny in Tomato Fruits

Abstract

Tomato fruits were harvested at 10, 15, 20, 25 and 35 days after anthesis and held in humidified ethylene-free air streams at 20°C. The time from anthesis to ripening (first appearance of red colour) was about 42 days in attached control populations but the time to first colour in detached fruits ranged from 43 days in 35-day fruits to 68 days in 10-day fruits. The delayed ripening in fruits detached at 10 days was largely explained by the further slow development of these fruits. One to four locules began to swell about 10 days after harvest and swelling continued slowly for up to 42 days after harvest. The swollen locules usually turned red 8-10 days after swelling ceased. The undeveloped portion faded to a yellow-green colour and eventually became necrotic. The swollen locules usually contained more germinable seeds than the remainder of the fruit tissue. Although some localized swelling was seen in detached 15-day fruits, the entire fruits ripened normally. Fruits of the same populations were treated with 2 g/l ethephon [(2-chloroethyl)phosphonic acid], both on the plant and following detachment. Ripening began earlier in detached fruits treated at all ages but the largest responses were found in fruits detached at 10,15 and 35 days. Ethephon advanced ripening in attached fruits only in those treated at 25 and 35 days after anthesis. Treatment with ethephon did not alter the appearance of detached 10-day fruits or the distribution of germinable seeds. A similar pattern of development was seen in detached fruits of the mutants rin and nor. The swollen locules of 10-day rin and nor fruits developed the characteristic colour and appearance of mature mutant fruits (yellow in rin, yellow-orange in nor) while the undeveloped parts of the fruits faded to a yellow-green colour and eventually became necrotic as in fruits of the normal strain. It is proposed that developing tomato fruits undergo a transition period which is largely completed by about 15 days from anthesis. During this transition period changes prerequisite for the eventual expression of ripening take place.