The effects of trellising, spacing and pruning on fruit yields and quality, disease incidences and production life of purple passion fruit at Thika, Kenya
The purple passion fruit is grown commercially in Kenya partly for the fresh market (both local and export markets), but most fruits are used for juice extraction. Although passion fruit has been grown in Kenya for a long time, very little attention has been paid to the cultural requirements of the passion fruit under Kenyan conditions. The general cultivation practices currently used in Kenya are those recommended in Australia and South Africa. This study was therefore, aimed at investigating the following cultural practices under Kenyan conditions:- 1. To determine the best way of training and pruning passion fruit. 2. To determine the spacing at which to grow passion fruit in Kenya. 3. To evaluate the effect 'of training, spacing and pruning in the incidence of diseases in the passion fruit. 4. To determine the economic life of the passion fruit under cultural practices listed above. Two experiments were conducted at two different sites at Thika, starting 1974. Experiment one (Trellising x Pruning), was conducted at the National Horticultural Research Station (0° 59'S 37° 04'E and 154S m above sea level) on a well drained deep highly weathered, fine textured and leached red friable clay-loamy soils. Two types of trellis (vertical and horizontal) were constructed. Trellising posts of 2.70 m long and 15 cm diameter spaced at 6 m interval in the rows were erected in holes of 60 cm deep. In the vertical trellis, single 14—gauge wires were fixed firmly on top of the posts. In the horizontal trellis, three parallel wires supported by T-pieces about 75 cm long were fixed at the top of the posts. One wire was fixed at the-centre, while other two wires run parallel at both ends of the T-piece. The seedlings were raised in polythene tubes. They were transplanted in April, 1974 when they were about three months old. They were spaced at 1.80 m between the rows and 3 m between the plants in the row. Training of the vines started one month after transplanting. Two healthy shoots close to the base of each plant were trained along sisal strings tied at the base of the vine and at th3 wire on top. All other side shoots were removed as they appeared. When these shoots reached the wire, they were twined along the wire in opposite directions and were allowed to develop side shoots (laterals) from the top of the wire. Four pruning treatments (severe, light, selective and no pruning) were also applied. Tendrils were removed fortnightly from the fruiting laterals in the severe, light and selective pruning treatments. In the severe pruning treatment, all laterals were cut back to within 15 cm of the wire 13 months after transplanting. In the light pruning treatment, all laterals were also cut back to about 60 cm from the ground level 13 months after transplanting. These operations were repeated yearly during long rains. In the selective pruning treatment, each fruiting lateral was renewed by cutting it % back to a newly developing side shoot close to the main leader on the wire once it had borne its last fruit. This was continuous throughout the study period. In the no pruning treatment, after training the main leaders on the wire, only those fruiting laterals lying on the ground were cut to about 15 cm from the ground level. No other pruning operations were done. Shoot growth, time of flower opening, fruit set and fruit development and development of new growth after severe pruning were observed. Ripe fruits were analysed to determine the weight of fruits, yield of pulp and juice. Disease incidences were also recorded. The vines were stumped to 45 cm after 2^ years of harvest. The shoots took 90 to 100 days to reach the wire from transplanting. Flowers open between 7.00 and 9.00 a.m. Flowers not covered with paper bags had higher fruit set than those which were covered. Fruit took 88 days from anthesis to full maturity. The non-pruned vines gave higher fruit yields than those pruned during the first year. They declined in fruit production after 15 months of harvest. They were also severely infected by fungal diseases Dn both laterals and fruits than those from pruned vines. The selective and light pruned vines were more productive than the non—pruned ones from the second year. Severely pruned vines were also healthy and productive until after the second severe pruning,when they started declining both vegetatively and in fruit production. The pruned vines had mor;e marketable fruits, heavier fruits with higher pulp and juice content than those unpruned. The stumped vines dried up. The vines on the vertical trellis had more fruit yields and were less infected by fungal diseases than those on the horizontal trellis. Experiment two was conducted at Swani Estate (l° 01* S 37° 02'E) on a similar type of soil as in experiment one. The vines '’are trained on the vertical trellis. Supplementary irrigation was supplied during dry periods. Two spacing treatments were used (narrow and wide spacing). In the narrow spacing, plants were spaced at 1.20 m between the rows and 3 m between the plants in the row; while in the wide spacing, plants were spaced at 1.80 m between the rows and 3 m between the plants in the row. The pruning treatments and operation procedures are the same as in experiment one. Flower bud appearance and onset of flower opening vas observed. Shoot growth, development of new growth after severe pruning, fruit yield records, fruit quality, disease incidences were recorded as in experiment one. In this experiment most fruits were plucked from the vines when they attained purple colour. The flower bud took 46 days to open. The non pruned vines outyielded pruned ones in the first year, after which they declined. The selectively and lightly pruned treatments were productive throughout the experimental period. They had heavier and juicier fruits than the non pruned ones. Narrow spacing had higher fruit yields but severely infected by fungal diseases than the wide spacing. It was concluded that due to the rapid shoot growth, training of shoots should etart immediately after transplanting. The light and selective pruning lengthened the productive life of the vines and improved fruit quality. The use of the vertical trellis in Kenya should continue. Narrow spacing should be practiced by small scale farmers. Supplementary irrigation is beneficial during the dry periods.
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