Effects of therapeutants and temperature on pollen germination, pollen tube growth and fruit set in fruit crops : a thesis presented in partial fulfilment of the requirements for the degree of Master of Horticultural Science at Massey University

This study involved assessments of therapeutant effects on pollination and fruit set; of temperature effects on pollen germination and pollen tube growth in apples, peaches and kiwifruits; of flowerage effects on pollen germination and pollen tube growth in kiwifruit styles; and of hand pollination effects on fruit set, fruit weight and seed numbers per fruit in kiwifruit vines. From the point of view of their in vitro effects on pollen germination therapeutants can be listed in order of decreasing inhibitory effect as follows: (a) for apples - mancozeb plus dinocap, triforine, dichlofluanid, bupirimate, bayleton, citowett R captan and mancozeb; (b) for peaches - triforine, vinclozoline, streptomycin plus triforine, mancozeb, captafol, iprodione, dichlofluanid, streptomycin and benomyl; and (c) for kiwifruits - dichlofluanid, captan and vinclozoline. However, it appeared that while in vitro a therapeutant was very inhibitory, the application of a spray to anthers in an intact flower did not affect the germination of pollen subsequently released by those anthers. Fungicides proven to be toxic to pollen in vitro did not necessarily produce similarly toxic effects in vivo. Reasons for such varying effects of fungicides on pollen germination and pollen tube growth in vitro and in vivo are suggested. At 24 hours after pollination the number of pollen tubes growing more than 1/2 the style length of kiwifruit (Hayward) flowers one to two days old were 38% and 27% higher than in flowers less than one day old and more than three days old respectively. In apples 5 sprays of either bayleton or captan, 3 sprays of either of the therapeutants mancozeb, mancozeb plus dinocap, and triforine and a wetting agent citowett R applied during bloom period caused no effect in fruit set in Golden Delicious trees; and 3 bupirimate sprays during bloom period had no effect on the fruit set in Splendour trees. In peaches 6 sprays of either captafol, or benomyl or iprodione, 5 sprays of either mancozeb or vinclozoline or streptomycin or triforine during bloom period caused no effect on fruit set in Golden Queen trees. Three sprays of streptomycin or dichlofluanid caused no effect but 3 sprays of triforine, triforine plus streptomycin or of ethephon caused 50%, 70% and 90% reduction in fruit set in Red Haven peach trees. In kiwifruits 3 sprays of either dichlofluanid, captan or vinclozoline reduced seed numbers per fruit by 37% but did not affect fruit set or fruit weight. Thus in vitro and in vivo studies were useful in determining therapeutant effects on pollen but did not necessarily provide information on their effects on fruit set in apple, peach and kiwifruit and on fruit weight and seed numbers per fruit in kiwifruit. The germination of both apple and peach pollen was higher at 24°C than at 16°C, 20°C, 28°C and at 32°C. After 18 hours incubation pollen tubes were longer at 28°C and at 32°C than at 16°C, 20°C and 24°C. In vivo studies with kiwifruit (Matua) pollen showed that pollen germination at 14°C, 18°C, 22°C and 26°C did not differ significantly. Temperatures both higher and lower than the temperature range 18 to 22°C were found to be inhibitory to pollen tube growth in kiwifruit (Hayward) styles. Hand pollination of flowers did not influence percentage fruit set but increased fruit weight and seed numbers per fruit in kiwifruit (Hayward) vines. Because fruit weight was positively correlated with seed number per fruit in fruits from both bee pollinated and bee plus hand pollinated flower clusters, supplementary pollination may play an important role in the production of fruit in kiwifruit orchards

Vegetative Growth, Fruit Set, Yield and Fruit Quality of "Le-Conte" Pear Grown Under Calcareous Soil Conditions as Affected by Different Levels of Nitrogen, Phosphorus and Potassium

"Le-Conte" pear fruiting trees grown in newly reclaimed soils were fertilized with different levels of nitrogen, phosphorus and potassium fertilization during three successive seasons of 2006, 2009 and 2010. However, results were calculated for the two seasons of 2009 and 2010. Tree vegetative growth (shoot length and diameter and leaf area), fruit set, yield increased significantly with increasing fertilization level. Fruit quality was increased significantly with increasing fertilization rate. The results also indicated that increasing N, P and K fertilization level lead to a gradual increment in leaf N, P and k content. Total sugars in fruits increased significantly with increasing the fertilization levels. On the other hand, starch decreased gradually with increasing the fertilization levels. The most effective level (650g. Ammonium nitrate + 325g. Potassium sulphate + 600g. Calcium superphosphate) leads to the highest vegetative growth, mineral leaf content, fruit yield and the best fruit quality as compared with other levels of fertilization. The lowest vegetative growth, yield and fruit weight and dimensions were recorded at the lowest level (250g. Ammonium nitrate + 125g. Potassium sulphate + 200g. Calcium superphosphate)

Some factors influencing flowering and fruit-set of clementine mandarin

A four-year research study conducted in center Sardinia on clementine mandarin has evidenced that flowering and subsequent fruit-set can be affected by several factors, i.e., growth substances, light intensity and temperature before flowering. Particularly it has been shown that gibberellic acid sprayed during flower differentiation reduced the number of flowers/ square meter of canopy,but increased the number of leafy inflorescences and the fruit-set percentage. Alar sprayed in the same conditions increased the number of flower/square meter and reduced the number of leafy inflorescences and the fruit-set percentage. Low light intensity obtained by shading trees with large cages covered with nets of black nylon decreased the number of flowers and leafy inflorescences, but no clear effects were found on the fruit-set percentage. Warm temperatures before flowering increased the number of flowers/square meter, but decreased the fruit-set percentage

Effects of Growth Regulators on Fruit Set and Growth of the Acerola (Malpighia glabra L.)

The low natural fruit set of acerola in Hawaii, attributed to absence of pollen transferring agents, indicated the feasibility of growth regulator application to induce fruit set. Among the several growth regulators tried initially, 4-chlorophenoxyacetic acid (PCA) and indolebutyric acid ( IBA) were found to be effective in promoting fruit set, the f rmer being more efficient over a wider range of concentration. PCA exhibited some phytotoxic effects in the nature of leaf curling, yellowing, and even death of young vegetative tips. Phytotoxic effects were reduced in severity with decrease in concentration. lBA at 100 ppm effected approximately 60 percent fruit set without any apparent phytotoxic effects. Under field conditions the satisfactory fruit set and lack of phytotoxic effects with IBA at 100 ppm make this a highly desirable compound, but the wide use of it may be prohibited by its high cost. On the other hand, PCA at 50 ppm can induce as much fruit set as lBA at 100 ppm, and phytotoxic effects are mild with early recovery. Furthermore, the very low cost of this material makes its use economically feasible

Stochastic dynamic simulation of fruit abortion: a case study of sweet pepper

Abortion of reproductive organs diminishes yields in many crops. In indeterminate greenhouse crops, alternating periods of fruit abortion and fruit set exist, resulting in fluctuations in fruit yield. Factors affecting the level of abortion are e.g., the supply and demand for assimilates (source and sink strength, respectively), temperature and cultivar. However, simulation of fruit abortion is still a weak part of crop simulation models. Variation in fruit abortion exists between plants, which results in differences in the timing and the number of set fruits. Therefore, simulating fruit abortion with variation could give more realistic simulation results. The probability of a fruit to abort should be related to factors like source strength and sink strength. The more favourable the circumstances are for fruit abortion, e.g., low source strength or high sink strength, the more likely it is that the fruit aborts. Survival analysis estimates parameters quantifying the influence of explanatory variables on the abortion rate. Time-varying explanatory variables can be used in the analysis. In a case study, we used survival analysis to analyse a data set with observations on flowering, fruit abortion and fruit harvest for sweet pepper. Source and sink strength were used as explanatory variables. The resulting equation determining the probability of abortion per day was implemented in a simple simulation model to simulate fruit set. The model output, as an average of 100 plants, showed similar timing in the fluctuations in fruit set as the observations, although the amplitude of the fluctuations was in some cases underestimated. The percentage fruit set was simulated correctl

Regulatory Features Underlying Pollination-Dependent and -Independent Tomato Fruit Set Revealed by Transcript and Primary Metabolite Profiling

Indole Acetic Acid 9 (IAA9) is a negative auxin response regulator belonging to the Aux/IAA transcription factor gene family whose downregulation triggers fruit set before pollination, thus giving rise to parthenocarpy. In situ hybridization experiments revealed that a tissue-specific gradient of IAA9 expression is established during flower development, the release of which upon pollination triggers the initiation of fruit development. Comparative transcriptome and targeted metabolome analysis uncovered important features of the molecular events underlying pollination-induced and pollination-independent fruit set. Comprehensive transcriptomic profiling identified a high number of genescommonto both types of fruit set,amongwhich only a small subset are dependent on IAA9 regulation. The fine-tuning of Aux/IAA and ARF genes and the downregulation of TAG1 and TAGL6 MADS box genes are instrumental in triggering the fruit set program. Auxin and ethylene emerged as the most active signaling hormones involved in the flower-to-fruit transition. However, while these hormones affected only a small number of transcriptional events, dramatic shifts were observed at the metabolic and developmental levels. The activation of photosynthesis and sucrose metabolism-related genes is an integral regulatory component of fruit set process. The combined results allow a far greater comprehension of the regulatory and metabolic events controlling early fruit development both in the presence and absence of pollination/fertilization

Pollination and Fruit Set in the Yellow Passion Fruit

The development on the use of the yellow passion fruit (Passiflora edulis forma flavicarpa Degener) for beverage, ice cream, sherbet, pastries, and other confectionaries has resulted in increased plantings of this crop in Hawaii. With this expansion, various cultural problems have been brought to the attention of the Hawaii Agricultural Experiment Station by farmers growing this crop and by the processors of passion fruit juice. In the studies reported here factors which may limit fruit set, fruit production, and juice yield have been given special attention

Chemical thinning of 'Conference' pears

The increasing difference in the market value of small and larger sized ‘Conference’ pears (>65 mm) and the high labour costs for hand thinning, makes it interesting for growers to find a cheaper and reliable method for thinning pear trees. In 2007, 2008 and 2009 trials were carried out to test the thinning efficacy of several chemicals. Fruit set was only significantly reduced by a two-fold application of ammonium thiosulphate (ATS) or by a tankmix application of 6-benzyladenine (BA) and 1-naphtalene acetic acid (NAA). Unfortunately, russeting of ‘Conference’ pears was augmented by the treatments with ATS during bloom. Tankmix applications of NAA + BA, applied at an average fruit diameter of 8.8 mm, resulted in a severe overthinning of the trees in 2008. However, the same treatments applied at an average fruit diameter of 14.7 mm had much less of a thinning effect. In 2009 adequate thinning was obtained with lower concentrations of BA+NAA applied at 8-10 mm fruit diameter. Surprisingly, the reduction in fruit set by BA+NAA did not result in a proptional increase in the average fruit weight at harvest. In some treatments average fruit weight was even reduced compared to that of the hand-thinned trees, a size-reducing effect that was attributed to NAA. In conclusion, BA+NAA seems to thin ‘Conference’ pears more strongly than BA alone. However, the addition of NAA to BA has the disadvantage of a diminishing effect on the increment of fruit size, i.e. fruit size increased less than expected on basis of the reduction in crop load. Additional research will be carried out to further optimise the developmental stage, weather conditions, and concentrations at which a BA and NAA must be applied to obtain the desired level of thinning and gain in yield percentage of fruits over 65 mm in diameter

EDITOR'S CHOICE: REVIEW: Trait matching of flower visitors and crops predicts fruit set better than trait diversity

Understanding the relationships between trait diversity, species diversity and ecosystem functioning is essential for sustainable management. For functions comprising two trophic levels, trait matching between interacting partners should also drive functioning. However, the predictive ability of trait diversity and matching is unclear for most functions, particularly for crop pollination, where interacting partners did not necessarily co-evolve. World-wide, we collected data on traits of flower visitors and crops, visitation rates to crop flowers per insect species and fruit set in 469 fields of 33 crop systems. Through hierarchical mixed-effects models, we tested whether flower visitor trait diversity and/or trait matching between flower visitors and crops improve the prediction of crop fruit set (functioning) beyond flower visitor species diversity and abundance. Flower visitor trait diversity was positively related to fruit set, but surprisingly did not explain more variation than flower visitor species diversity. The best prediction of fruit set was obtained by matching traits of flower visitors (body size and mouthpart length) and crops (nectar accessibility of flowers) in addition to flower visitor abundance, species richness and species evenness. Fruit set increased with species richness, and more so in assemblages with high evenness, indicating that additional species of flower visitors contribute more to crop pollination when species abundances are similar. Synthesis and applications. Despite contrasting floral traits for crops world-wide, only the abundance of a few pollinator species is commonly managed for greater yield. Our results suggest that the identification and enhancement of pollinator species with traits matching those of the focal crop, as well as the enhancement of pollinator richness and evenness, will increase crop yield beyond current practices. Furthermore, we show that field practitioners can predict and manage agroecosystems for pollination services based on knowledge of just a few traits that are known for a wide range of flower visitor species

Factors affecting reproductive success in three entomophilous orchid species in Hungary

The reproductive success of orchids is traditionally estimated by determining the fruit-set of individuals. Here, we investigated both the fruit and the seed production of three orchid species and the factors that may affect individual fruit-set, like pollination strategy, individual traits or the annual amount of precipitation. The species [Dactylorhiza sambucina (L.) Soó, Dactylorhiza majalis (Rchb.) P. F. Hunt & Summerhayes and Platanthera bifolia (L.) L. C. M. Richard] were studied in three consecutive years (2010–2012) in the Bükk Mountains, Hungary. All three species were proved to be non-autogamous by a bagging experiment. Data analyses showed significant differences between seed numbers but not between fruit-sets of species. There was no statistical difference in individual reproductive success between wet and dry years, however, the effect of the annual amount of precipitation is significant on the population level. Comparison of published fruit-set data revealed accordance with our results in P. bifolia, but not in D. sambucina and D. majalis. We assume that the surprisingly high fruit-set values of the two Dactylorhiza species may be due to the fact that the pollination crisis reported from Western European countries is not an actual problem in the Bükk Mountains, Hungary