Improving tomato harvest index by controlling crop height and side shoot production

Given the constraints on physical space, energy supply, and labor availability, crop production efficiency must be maximized if a sustainable supply of food is to be produced on lunar and planetary space stations. In the modules designed for plant growth, crop production efficiency or the harvest index (HI, fruit weight/total plant weight) must be calculated on a cubic volume basis because the physical space allocated for plant growth will be limited in three dimensions. In order to increase HI, tomato plant architecture could be modified to reduce the extent of internode elongation and side shoot production. To test this hypothesis, plants were treated with the growth retardant paclobutrazol (PAC) and topped after the second flower cluster. PAC reduced plant height at harvest by 29% and total vegetative shoot growth by 28%. Fruit yield was reduced by 12%, although the greater reduction in vegetative growth by PAC resulted in an increased HI from 0.53 to 0.58 when calculated on a gram fresh weight basis. Yield/m3 of growing space utilized increased 23% with PAC treatment. The leaf axils of tomato plants grown in a single truss system were treated with the chemical pruning agent Off-Shoot-O (OSO), a mixture of short chain fatty acid methyl esters. OSO significantly reduced the number of side shoots/plant, increased fruit yield by 12%, and increased the HI from 0.71 to 0.77 compared to hand-pruned plants. Untreated plants required three manual pruning operations during the production period; plants treated with OSO were pruned only once at the time of application for a significant savings in labor. The results of both experiments clearly demonstrate that HI of tomato can be increased by reducing internode elongation and preventing side shoot development.