P.R.C. Castro
Sprays of succinic acid-2.2-dimethylhydrazide (SADH) or (2-chloroethyl) trimethylammonium chloride (CCC) can be used to increase the yield of tomato plants and to cause the fruits to ripen more uniformly, thus allowing a shorter harvest period. The most effective treatment were those in which 2.500 ppm of SADH was applied at the first of fourth true leaf stage of growth or at both of these times. Concentration of harvest was improved and early yield was increased by subsequent application of 5.000 ppm SADH as a flower "cut-off" spray after desired fruit set had been achieved. The latter treatment has desirable implications for mechanical harvesting, since it virtually eliminated green fruit "pick-out" and slowed vegetative growth, thus causing a more concentrated harvest because of more rapid fruit maturation. The yield increases are attributed to a combination of effects including resistance to water and heat stresses, more flowers per cluster and thus more fruits per plant (Table 1) (Read and Fieldhouse, 1970).

To study the influences on fruiting, CCC (2.000 ppm), SADH (3.000 ppm) gibberellic acid (GA) 200 ppm, and (2-chloroethyl) phosphonic acid (CEPA) 200 ppm were applied in tomato plants at the fourth true leaf stage of growth. The treatments did not affect the total weight of tomato fruits. These growth regulators did not promote changes in fruit number. Application of CCC and CEPA did not affect the fruit weight average, however, spraying with SADH and GA reduced the fruit weight average (Castro and Malavolta, 1976).

It was studied the relationships between growth regulators, mineral nutrition, osmotic potential, and incidence of blossom-end rot (BER) in tomatoes. The chemicals were applied in tomato plants at the fourth true leaf stage of growth and ammonium sulphate was used to promote the occurence of BER. GA (100 ppm) promoted higher incidence of BER and CCC (2.000 ppm) reduced the occurrence of the physiological disease in relation to control (figure 1A and 1B) (Castro e Malavolta, 1977). Higher levels of N, Ca, and Mg occurred in the stems of plants sprayed with CCC (Malavolta et al., 1975). Treatments with 6-furfurylamino purine (5000 ppm), SADH (4,000 ppm), and CEPA (200 ppm) presented an increase in N level in the stem. CEPA also increased Ca content in stems. These growth regulators did not alter the levels of macronutrients in leaves of tomatoes in relation to control (table 2) (Castro et al., 1979). Plants treated with GA and SADH had a lower (more negative) leaf osmotic potential under water deficit in the soil (table 3) (Castro, 1976).

The auxin 2-hydroxymethyl 4-chlorophenoxyacetic acid was applied at concentrations of 150 and 300 ppm by spraying directed to the clusters in the moment of the opening of the two first flowers in the first cluster. This growth regulator at concentration of 300 ppm increased the average weight of tomato fruits in the four initial harvests. It was noted also a concentration in production of fruits in relation to the control (figure 2) (Castro and Churata-Masca, 1973).

Castro, P.R.C. (1980). PLANT GROWTH REGULATORS IN TOMATO CROP PRODUCTION. Acta Hortic. 100, 99-104
DOI: 10.17660/ActaHortic.1980.100.13

Acta Horticulturae