Wen-Ju Yang

Differential responses to short-term salinity stress of heat-tolerant cherry tomato cultivars grown at high temperatures

Although many new tomato cultivars with various degrees of heat-tolerance have been released, year-round tomato production in subtropical lowlands is still challenged by summer heat and an increasing risk from salinity stress. Little information about the simultaneous effects of heat and salinity on growth and fruiting in tomatoes is available. It was hypothesized that cultivars which perform better in high temperatures are also more tolerant to salinity stress. Two highly heat-tolerant cultivars, ‘Tainan ASVEG No. 19’ (TA19) and ‘Taiwan Seed ASVEG No. 22’ (TSA22), and one moderately heat-tolerant cultivar, ‘Hualien ASVEG No. 21’ (HA21), were grown under high temperature conditions and were irrigated with a 0, 50, 150, or 200 mM NaCl solution for 20 days. Vegetative growth, fruiting behavior, and fruit quality were monitored. Number of leaves, leaf area, shoot fresh and dry weights, and root fresh weight were generally decreased with increasing level of salinity stress, but root dry weight was not affected, resulting in an increase in root to shoot ratio in all three cultivars. Yield was also decreased by salinity treatments in all three cultivars due to reduced number of flowers, fruit set, and fruit size. The highly heat-tolerant ‘TA19’ had the lowest vegetative growth and the highest yield under the high temperature condition, but the yield was strongly suppressed by the short-term mild salinity treatment. On the other hand, vegetative growth was little affected and the degree of yield reduction was less intense with the short-term mild salinity treatment in the moderately heat-tolerant ‘HA21’. The result indicated that effects of heat stress and salinity stress are not additive and differential responses to salinity under high temperatures exist among cultivars with various degrees of heat-tolerance.

Partial defoliation and runner removal affect runnering, fruiting, leaf photosynthesis and root growth in ‘Toyonoka’ strawberries for subtropical winter production

Removing runners and old leaves are two major routine and labor consuming tasks in winter strawberry (Fragaria × {ptananassa} Duch.) production in subtropics. However, the potential negative effects of defoliation has not been evaluated. We studied the effects of partial defoliation and runner removal on plant growth, leaf photosynthesis (Pn), and yield in field-grown or potted strawberry plants (‘Toyonoka’). The treatments were consisted of partial defoliation by removing leaves older than 45 days (PD), removing all runners (DR), PD + DR, and the control (CK). Treatments were applied weekly from mid-November until early March. DR promoted yield and number of fruits for the first harvest cycle but not for the second harvest cycle. Multiple linear regressions indicated that leaf area had greater overall effects on runnering and fruit traits than the existence of runners. The leaf Pn was not responsive to DR but a transient increase in Pn was consistently detected on the remaining leaf after each PD treatment. The compensatory increase in Pn was only detectable within 1 days after each PD treatment, indicating that the actual compensation for partial loss of functioning leaf area may be negligible. Crown dry weight was less affected by canopy manipulation than growth and dry weight of roots. Our results indicated that yield of strawberry in Taiwan’s subtropical climate can be improved by removing runners while maintaining a greater leaf area with less severe defoliation.

Prevention of natural flowering in pineapple (Ananas comosus) by shading and urea application

The year-round production of pineapple (Ananas comosus var. comosus) is often interrupted by natural flowering during winter in Taiwan. A stable and promising technique for preventing natural flowering is required. In this study, we have tested the effect of shading and urea application on the flowering of pineapple. Shading 90% of sun light(s) before mid-November delayed the natural flowering of pineapple and the delay was affected by the plant age. For pineapples planted less than 11 month before mid-November, applying 1% urea plus shading treatment (SN) completely inhibited natural flowering. All the flowering-inhibited plants could be forced to flower by applying calcium carbide. Long-term shading might result in a decreased number of fruitlets within a fruit. However, 6 weeks of recovery before forcing flowering was sufficient for plants to produce fruits with quality equal to that of the control plants. In winter, pineapple plants that were prone to flowering tended to accumulate more leaf starch and increase their C/N ratio. The SN treatment increased the leaf nitrogen concentration and thus effectively maintained a low leaf C/N ratio. Furthermore, flowering-inhibited plants exhibited a constantly low level of leaf starch during the winter and their flowering forced by calcium carbide did not accompany with leaf starch accumulation.

Invading time of Colletotrichum gloeosporioides affects fruit drop and infection rate in ‘Irwin’ mango (Mangifera indica L.)

To improve mango anthracnose management in Taiwan, the critical timing when anthracnose invades mango panicles is a priority subject. A 3-years field study was conducted by inoculating panicles at different developmental stages with 105 conidia/mL suspensions. Invading panicles at the full blooming stage resulted in 67.2% of panicles without setting any fruit and 61.1% of the fruitlets dropped, highest latent infection rate in the unripe fruits, and highest infection rate and largest infected area in the ripe fruits during the postharvest stage. Based on the data provided, we concluded that full blooming stage was the critical stage for C. gloeosporioides control in mango production, and suggest that controlling the population of field pathogens before full blooming stage should be emphasized in routine practice.