Lin, S., W. L. George and W. E. Splittstoesser.

Parthenocarpy and the ability to set fruit under high temperature conditions.

 

The tomato cultivar Severianin from the USSR has the ability to set seedless (parthenocarpic) fruit in some environments. Parthenocarpic fruit of Severianin appear normal with complete locule fill even in the absence of seed. The parthenocarpic trait of

Severianin is controlled by a single recessive gene, pat-2 (Pilouze and Maisonneauve, TGC 28:12).

            In controlled temperature studies, Severianin exhibited excellent fruit-setting heat tolerance as did Clld, a heat tolerant line from AVRDC, Taiwan when compared to Ohio M-R 13, a heat sensitive greenhouse cultivar. Severianin and Clld set about 70% more fruit than Ohio M-R 13 when grown at constant 26°C (Table 1).

 

Table 1.            Percentage of fruit-set of various tomatoes grown under favorable and

unfavorable night temperatures.

 

Temperature                                                                 Clld

(day/night)                    Sevenianin                    (% fruit set)                  Ohio M-R 13

26°C/l6°C                        54                                   69                                 58

 

26°C/26°C                        52                                   54                                 36

 

The unusually high temperatures during the summer of 1980 provided an opportunity to observe fruit-set under field conditions. Several genetic populations had been transplanted into the field on June 12, 1980, in Urbana, Illinois (Table 2). For the remainder of June and July daily temperatures regularly ranged from night lows of 20-25°C to day highs of 30-38°C. Most of the fruits (early production) that set during that period were parthenocarpic. Set of early fruit was recorded from July. 25-29, 1980. For example, in the BC, F1 (Severianin x Ohio M-R 13) x Severianin, 44 of 93 plants set early fruit of which 38 (86%) were parthenocarpic segregates, whereas, in the BC, F1 (Severianin x Clld) x Severianin, 89 of 96 plants set early fruit of which 48 (54%) were parthenocarpic segregates. Thus, the parthenocarpic gene, pat-2, is contributing to some of the heat tolerant fruit-setting ability particularly in the cross with Ohio M-R 13.

            In conjunction with inheritance studies of the parthenocarpic trait during the summer of 1980 the genetic populations were also classified into plants with early fruit—set vs. plants without early fruit set. In the progenies of the heat-sensitive line Ohio M-R 13 x Severianin, the ability to set early fruit under high temperatures appeared to be controlled by a single recessive gene (pat-2), however, the segregation in the progenies from the heat-tolerant line Clld x Severianin did not fit this hypothesis (Table 2).

 

Table 2. Inheritance of early fruit—set under unfavorable environments.Z

 

                                                Number of plants

           

                                                  With              Without                    X2

                                                 early                early                 F2 (3:1)

            Population                    Total    fruit-set         fruit-set                 BC(1:1)           Probability

            Severianin                     20        20                    0

 

            Ohio M-R 13               31        0                      31

            F1                                 72        4                      68

            F2                               155      45                    110                  1.34                 0.10-0.25

            BC-Severianin              93        44                    49                    0.27                 0.50-0.75

            BC-Ohio M-R 13        91        5                      86

 

            Clld                             24        6                      18

            F1                                 46        39                    7

            F2                                137      112                  25                    235.30              < 0.01

            BC-Severianin              96        89                    7                      70.04                < 0.01

            BC-Clld                       94        71                    23

               

 ZTomatoes were transplanted in the field on June 12. Plants with early fruit-set were recorded from July 25-29, 1980.

 

The Clld x Severianin progenies had an excess of plants with early fruit set. These results suggest that pat-2 can contribute to the ability to set fruit under high temperatures. Clld has been selected for genes other than parthenocarpy that improve fruit setting under high temperatures. Thus, the selection of lines with a strong tendency of parthenocarpy and other genes for heat tolerance may lead to the development of tomato lines with abilities to set fruits under wide environmental regimes.