Increased Air Temperature and Tomato Fruit Set and Development

Pollination and fruit set are vital stages in vegetable production. Understanding factors that influence fruit set is major first step in managing the process (including on farms).
Tomato is a significant crop in Ohio and worldwide. While tomato’s temperature optima exceed those of other crops, it is worth considering the extent to which these limits have been reached in 2012, especially in high tunnel systems. In fact, temperature appears to be one of a number of environmental factors with a strong influence on tomato fruit set — but at what stage in what way? Explanations are possible only through controlled study.
Two teams engaging S. Sato and colleagues at NCSU and Chiba and Osaka Prefecture Universities in Japan sought to describe linkages between moderately elevated temperatures and tomato flower and fruit development. To begin, they selected nine cultivars and subjected them to either moderately elevated (approx. 90°F/79°F day/night) or control (approx. 79°F/72°F day/night) temperatures in environmentally controlled chambers (Sato et al., 2004). Analyzing flowers and fruit produced by both experimental groups, they discovered that the numbers of undeveloped and aborted flowers were greatest in the high temperature group. Of fruit from flowers that did develop, the percentage lacking seeds also increased sharply at higher temperatures.

Aiming to further explain their findings, the scientists completed a second study (Sato et al., 2006) using a similar approach with important modifications. This time they focused on male reproductive development as one component of flower and subsequent fruit development. Temperature set points were similar to those in the first study but a single cultivar was grown in two phytotron greenhouses. Also, measures of plant growth, pollen viability and metabolic functions were included. Vegetative growth was relatively unaffected but not so with other variables. For example, high temperatures led to a 77% reduction in fruit set, a 62% reduction in the number of pollen grains released and a 78% reduction in viable pollen grains. Also, a reduction in glucose and fructose content in developing flowers hindered pollen grain development and reduced pollen viability. The authors speculated that these disruptions can interfere with later events such as fruit set, seed formation and fruit development.

Based on these findings, overall, it is reasonable to conclude that supra-optimal temperatures hinder tomato plant growth less than fruiting – specifically, flower development, pollen abundance and viability and seed production. For growers, fewer fruit of questionable quality are possible at above-optimal temperatures.