Studies on Flowering Habit, Pollen Morphology and Activity of Irwin Mango (Mangifera indica L.)

Flowering habit, morphology and activity of pollen grains of Mangifera indica L. cv. Irwin were studied. Most of the flowers opened at night while dehiscence was mostly active between 10:00 and 14:00. There was no difference between male and hermaphrodite flowers in anthesis and dehiscence. No significant difference existed in pollen yield between male and hermaphrodite flowers. Pollen grains sampled from hermaphrodite flowers were rounder in shape and 3.5% greater in volume than pollen from male flowers. There was no difference in sculpture of exine between pollen from male and hermaphrodite flowers. Germination percentage of pollen from hermaphrodite flowers was much higher than from male flowers. Fluorochromatic reaction indicated the viability of pollen grains from both male and hermaphrodite flowers decreased rapidly about 10 hours after shedding.

Morphological Studies on Anther and Pollen Grains and in vitro Pollen Germination of Litchi chinensis Sonn.

Differences in anther histology and pollen morphology between male, hermaphrodite functioning as male and hermaphrodite functioning as female flowers of Litchi chinensis cv. Hak Ip and Yu Her Pau were investigated. Undegeneration of septum and tapetum occurred in the mature anthers of hermaphrodite functioning as female flowers. There is no difference between flower types in endothesium cell wall and cutin deposition on epidermal cells of anthers. Differences in pollen size were noticed between Hak Ip and Yu Her Pau, indicating a useful index for variety identification. Abnormal pollen grains were found from hermaphrodite functioning as female flowers. Optimal sucrose concentrations in medium ranged from 10 to 15% fro pollen germination but 5 to 10% for pollen tube elongation. 300 ppm calcium nitrate accelerated pollen tube elongation but did not increase germination percentage. Optimal pH for pollen germination was 5 to 7 for Hak Ip and 5 to 6 for Yu Her Pau. Pollen tube grew best on medium with pH 5 to 8. Pollen germinated better at 25°C to 30°C. Hak Ip had higher percentage of pollen germination rate than Yu Her Pau.

Oral presentation
for the Centennial
Conference of the
American Society for
Horticultural Science
October 2003

Assessing the Effect of Spotted Tentiform Leafminer Injury to Apples

Kuo-Tan Li (1), Alan N. Lakso (1) and Jan P. Nyrop (2)
(1) Department of Horticultural Sciences, New York State Agricultural Experiment Station, Cornell University, Geneva, NY 14456
(2) Department of Entomology, New York State Agricultural Experiment Station, Cornell University, Geneva, NY 14456

Current integrated pest management guidelines (IPM) suggest two mines per leaf as a treatment threshold for spotted tentiform leafminer (STLM, Phyllonorycter blancardella F.). However, studies of STLM damage in apple trees are few and inconclusive. To evaluate the effects of STLM on leaf and canopy photosynthesis as well as fruit growth, experiments were carried out on McIntosh and Red Delicious apple trees with natural and simulated STLM injury. The results showed that a single STLM mine typically occupies about 0.5 cm2, or 2 to 2.5% of the area of an average leaf, yet the visual injury appears much more severe. We found no statistically significant effect on photosynthesis of up to 10 mines per leaf. The green tissue remaining within the mined area might continue to photosynthesize, thereby reducing the effect of the mined area. In addition, mining by STLM might increase the photosynthetic efficiency of leaf tissue around the mined area. Natural STLM injury distribution within the canopy was simulated on trees in the field by punching holes in leaves with hole punchers. Although treatment with nine mines per leaf could remove more than 20% leaf area from a single leaf, it reduced total canopy leaf area by only about 8%, and the canopy photosynthetic efficiency was not significantly affected. STLM injury did not influence l fruit size or quality, a result expected based on carbon balance modeling. However, natural STLM injury (averaging five mines per leaf) induced early, preharvest fruit drop in McIntosh trees. The result indicates that the current IPM threshold for STLM overestimates the impact of STLM in apple trees other than McIntosh. In comparison, thresholds for European red mite have been found to be much closer to the biological threshold for carbon-based reductions in fruit growth.

HortScience 38(5):768

Summer Pruning and Re-exposure Effects on Leaf and Whole Canopy Gas Exchange in Apple Trees

K.-T. Li, A.N. Lakso and R.Piccioni
Department of Horticultural Sciences, New York State Agricultural Experiment Station, Cornell University, Geneva, NY 14456, USA

Summer pruning of apple trees is used to increase the light penetration into the inner canopy to improve fruit color; however, summer pruning may also reduce fruit size. We hypothesize that removing healthy exterior shoots reduces the whole tree carbon supply in relation to pruning severity. If the crop load (i.e. demand) is high, fruit size and quality will be reduced. The effects of re-exposure by summer pruning on photosynthetic activity of shade leaves occurred until late in the growing season. This indicates that the re-exposure of heavily-shaded leaves after summer pruning cannot replace the role of exterior leaves removed by pruning. Whole canopy net CO2 exchange rates (NCER) were measured on 'Empire'/M9 trees with a commercial range of pruning severity. Reductions in NCER were as great as 60% in the most severe pruning. Canopy light interception was found to decrease slightly. The effects on canopy NCER thus appeared to be primarily related to reduced photosynthetic efficiency and secondarily to reduced light interception.

Summer Pruning Effects on Leaf and Whole Canopy Gas Exchange in Apple Trees

Kuo-Tan Li and Alan N. Lakso
Cornell University, NYS Agric. Exper. Sta., Geneva, New York, USA

Summer pruning is primarily used in apples to increase the light penetration into inner canopy to improve fruit color. However, summer pruning may reduce fruit size. We hypothesize that removing healthy exterior shoots reduces the whole-tree carbon supply in relation to pruning severity. If the crop load (i.e., demand) is high, fruit size and quality will be reduced. The effects of summer pruning on photosynthetic activity and recovery of shaded leaves after re-exposure were monitored on a range of exposures in canopies of "Empire" apple trees. The photosynthetic ability of leaves was positively related to its prepruning exposure. There was little recovery of photosynthetic activity of shade leaves until late growing season, indicating the re-exposure of shade leaves after summer pruning cannot replace the role of exterior leaves removed by pruning. Whole canopy net CO2 exchange (NCER) was measured on 'Empire'/M9 trees with a commercial range of pruning severity. Reductions in NCER were approximately proportional to pruning severity and % leaf area removed and were as great as 60% in the most severe pruning. Canopy light interception decreased slightly. The effects on canopy NCER thus appeared to be primarily related to reduced photosynthetic efficiency and secondarily to reduced light interception.

HortScience 34(3):548

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