Shoot development, chlorophyll, gas exchange and carbohydrates in lychee seedlings (Litchi chinensis)

Shoot growth, chlorophyll concentrations, gas exchange and starch concentrations were studied in lychee (Litchi chinensis Sonn.) seedlings of cultivar “Wai Chee” grown in a heated greenhouse at Nambour in subtropical Australia (27° S). We also examined the effects of shoot defoliation and root pruning on leaf expansion. Shoot growth showed a rhythmic cycle under constant greenhouse conditions, with a mean duration of flushing of 20 days and an interval of 10 days over three cycles. Shoots and leaves expanded in a sigmoidal pattern to about 80 mm and 500 cm2, respectively, for each flush. Starch concentrations of the lower stem and roots decreased as the young red leaves expanded, and increased as the fully expanded leaves turned dark green. Chlorophyll concentrations and net CO2 assimilation rate were highest in the fully expanded dark green leaves.Removing 50% of the area of each fully expanded leaf had little effect on the expansion of younger leaves, but total biomass of defoliated plants was only 60% of that of controls. In contrast, removing half the roots just before bud swelling reduced final leaf area by 80%. We conclude that the young shoot has relatively low rates of photoassimilation until the leaves are fully expanded and dark green, and depends on assimilates from elsewhere in the plant. During leaf expansion, translocation of assimilates to the shoot occurred at the expense of the roots

Effects of light availability on leaf gas exchange and expansion in lychee (Litchi chinensis)

Effects of photosynthetic photon flux density (PPFD) on leaf gas exchange of lychee (Litchi chinensis Sonn.) were studied in field-grown “Kwai May Pink” and “Salathiel” orchard trees and young potted “Kwai May Pink” plants during summer in subtropical Queensland (27° S). Variations in PPFD were achieved by shading the trees or plants 1 h before measurement at 0800 h. In a second experiment, potted seedlings of “Kwai May Pink” were grown in a heated greenhouse in 20% of full sun (equivalent to maximum noon PPFD of 200 μmol m−2 s−1) and their growth over three flush cycles was compared with seedlings grown in full sun (1080 μmol m−2 s−1). Young potted plants of “Kwai May Pink” were also grown outdoors in artificial shade that provided 20, 40, 70 or 100% of full sun (equivalent to maximum PPFDs of 500, 900, 1400 and 2000 μmol m−2 s−1) and measured for shoot extension and leaf area development over one flush cycle. Net CO2 assimilation increased asymptotically in response to increasing PPFD in both orchard trees and young potted plants. Maximum rates of CO2 assimilation (11.9 ± 0.5 versus 6.3 ± 0.2 μmol CO2 m−2 s−1), dark respiration (1.7 ± 0.3 versus 0.6 ± 0.2 μmol CO2 m−2 s−1), quantum yield (0.042 ± 0.005 versus 0.027 ± 0.003 mol CO2 mol−1) and light saturation point (1155 versus 959 μmol m−2 s−1) were higher in orchard trees than in young potted plants. In potted seedlings grown in a heated greenhouse, shoots and leaves exposed to full sun expanded in a sigmoidal pattern to 69 ± 12 mm and 497 ± 105 cm2 for each flush, compared with 27 ± 7 mm and 189 ± 88 cm2 in shaded seedlings. Shaded seedlings were smaller and had higher shoot:root ratios (3.7 versus 3.1) than seedlings grown in full sun. In the potted plants grown outdoors in 20, 40, 70 or 100% of full sun, final leaf area per shoot was 44 ± 1, 143 ± 3, 251 ± 7 and 362 ± 8 cm2, respectively. Shoots were also shorter in plants grown in shade than in plants grown in full sun (66 ± 5 mm versus 101 ± 2 mm). Photosynthesis in individual leaves of lychee appeared to be saturated at about half full sun, whereas maximum leaf expansion occurred at higher PPFDs. We conclude that lychee plants can persist as seedlings on the forest floor, but require high PPFDs for optimum growth

Effects of leaf, shoot and fruit development on photosynthesis of lychee trees (Litchi chinensis)

Changes in gas exchange with leaf age and fruit growth were determined in lychee trees (Litchi chinensis Sonn.) growing in subtropical Queensland (27° S). Leaves expanded in a sigmoid pattern over 50 days during spring, with net CO2 assimilation (A) increasing from –4.1 ± 0.9 to 8.3 ± 0.5 μmol m−2 s−1 as the leaves changed from soft and red, to soft and light green, to hard and dark green. Over the same period, dark respiration (Rd) decreased from 5.0 ± 0.8 to 2.0 ± 0.1 μmol CO2 m−2 s−1. Net CO2 assimilation was above zero about 30 days after leaf emergence or when the leaves were half fully expanded. Chlorophyll concentrations increased from 0.7 ± 0.2 mg g−1 in young red leaves to 10.3 ± 0.7 mg g−1 in dark green leaves, along with stomatal conductance (gs, from 0.16 ± 0.09 to 0.47 ± 0.17 mol H2O m−2 s−1).Fruit growth was sigmoidal, with maximum values of fresh mass (29 g), dry mass (6 g) and fruit surface area (39 cm2) occurring 97 to 115 days after fruit set. Fruit CO2 exchange in the light (Rl) and dark (Rd) decreased from fruit set to fruit maturity, whether expressed on a surface area (10 to 3 μmol CO2 m−2 s−1 and 20 to 3 μmol CO2 m−2 s−1, respectively) or on a dry mass basis (24 to 2 nmol CO2 g−1 s−1 and 33 to 2 nmol CO2 g−1 s−1, respectively). Photosynthesis never exceeded respiration, however, the difference between Rl and Rd was greatest in young green fruit (4 to 8 μmol CO2 m−2 s−1). About 90% of the carbon required for fruit growth was accounted for in the dry matter of the fruit, with the remainder required for respiration. Fruit photosynthesis contributed about 3% of the total carbon requirement of the fruit over the season. Fruit growth was mainly dependent on CO2 assimilation in recently expanded dark green leaves

Climate change effects on winter chill for tree crops with chilling requirements on the Arabian Peninsula

Fruit production systems that rely on winter chill for breaking of dormancy might be vulnerable to climatic change. We investigated decreases in the number of winter chilling hours (0–7.2°C) in four mountain oases of Oman, a marginal area for the production of fruit trees with chilling requirements. Winter chill was calculated from long-term hourly temperature records. These were generated based on the correlation of hourly temperature measurements in the oases with daylength and daily minimum and maximum temperatures recorded at a nearby weather station. Winter chill was estimated for historic temperature records between 1983 and 2008, as well as for three sets of synthetic 100-year weather records, generated to represent historic conditions, and climatic changes likely to occur within the next 30 years (temperatures elevated by 1°C and 2°C). Our analysis detected a decrease in the numbers of chilling hours in high-elevation oases by an average of 1.2–9.5 h/year between 1983 and 2008, a period during which, according to the scenario analysis, winter chill was sufficient for most important species in most years in the highest oasis. In the two climate change scenarios, pomegranates, the most important tree crop, received insufficient chilling in 13% and 75% of years, respectively. While production of most traditional fruit trees is marginal today, with trees barely fulfilling their chilling requirements, such production might become impossible in the near future. Similar developments are likely to affect other fruit production regions around the world

In vitro culture and its application on the cloning of guava (Psidium guajava L.)

In vitro cloning of guava was achieved on Murashige and Skoog (1962) basal medium (MS) enriched with cytokinins. Using nodal explant, which proved to be superior to the shoot tip explant in this study, the highest multiplication rate (total number of nodes per explant) was induced by 0.5 mg1-1 benzylaminopurine (BAP) after 4 weeks. Higher concentrations (2.0 mg 1-1) of isopentyladenine (2iP) significantly improved shoot proliferation. Combinations of BAP and naphthaleneacetic acid (NAA) did not induce shoot growth. No difference was noticed between the morphogenetic response of the nodal explants cultured on either MS basal media or olive medium (OM)

The relationship between fruit and leaf growth in lychee (Litchi chinensis Sonn.)

The relationship between fruit and leaf growth was investigated in lychee (Litchi chinensis Sonn.) in a series of experiments in subtropical Australia (lat. 27°S). Panicles were removed at flowering to encourage new leaf growth on half the branches of each tree during fruit development. Some of the trees were pruned every week to prevent all vegetative growth, to test the effect of flower removal alone without subsequent leaf growth. In other experiments, the effect of pruning 50% of the branches was studied, but the pruning was scattered across the tree, rather than on one side. The yields of pruned trees with or without leaf flushes were more than 50% of the yield of the control plots in ten out of eleven cases, indicating that new leaves on one branch did not usually compete with fruit on adjacent branches. Concentrations of starch declined from flowering to harvest, and were higher in the branches than in the leaves, twigs, trunk and roots. In contrast, the effects of pruning were generally small. Concentrations of starch in the branches were sometimes higher when leaf or fruit growth was suppressed after pruning compared with branches with new growth. There were also slightly higher concentrations of starch in branches with leafy shoots than in those carrying fruit. These results suggest that the new leaves and fruit are more dependent on current assimilation than on stored reserves. New leaves on one branch do not reduce fruit growth in adjacent branches

The relationship between yield and assimilate supply in lychee (Litchi chinensis Sonn.)

Experiments were conducted on lychee (Litchi chinensis Sonn.) in subtropical Australia (lat. 27° –29°S) to evaluate the role of assimilates on fruit retention. All the leaves of the last flush, all the leaves of the previous flush (about eight leaves per terminal shoot), or all the old leaves were removed from trees. Medium (3–5.cm diameter) or large branches (5–10.cm diameter) were girdled and defoliated after fruit set, and fruit retention compared with ungirdled and undefoliated branches. Other branches were girdled and defoliated between anthesis and fruit harvest. Finally, 20, 50 or 80% of the flowering panicles were defruited on large trees. Defoliated trees had 35 to 45% lower yields than the controls. This was despite the treatment with all the old leaves removed having a much lower leaf area index than the other defoliation treatments (1.7 vs. 2.3 and 2.8). Leaves next to the inflorescences are more important for yield than the older leaves. Fruit retention was very low on girdled branches that had been defoliated, especially when the leaves were removed in the first 20.d after anthesis. This suggests that the yields of girdled branches were determined by the availability of assimilates soon after fruit set. In contrast, the number of fruit retained on ungirdled branches was unrelated to the number of leaves, with defoliation having no effect on yield. Fruit on these branches were supported by resources from elsewhere in the tree. Thinned trees had similar yields to those of unthinned plots (65–82.kg tree–1). Thinning apparently increased fruit retention in the remaining clusters, under a higher leaf:fruit ratio. There were large differences in the concentrations of starch in the tree, and seasonal changes, with starch declining from flowering to fruit harvest. In contrast, there were only small responses to the treatments, suggesting that the fruit were mainly dependent on current photosynthesis. Photosynthesis in the leaves behind the fruit clusters was more important than photosynthesis in the older shaded leaves