Poor Fruit Set Research Articles

Anomalies in Structure, Growth Characteristics, and Nutritional Composition as Induced by 2,4-Dichlorophenoxy Acetic Acid Drift Phytotoxicity in Grapevine Leaves and Clusters

Drift hazards and the effects of 2,4-dichlorophenoxy acetic acid (2,4-D) spray drift on woody perennials have been commonly observed since its discovery in the 1940s; however, 2,4-D-induced phytotoxicity, morphogenesis, and structural and compositional anomalies of their vegetative and reproductive structures are not well understood. Healthy and 2,4-D-injured shoots of grapevine (Vitis vinifera L.) from a commercial vineyard experiencing persistent drift were compared. The morphoanatomy of healthy and 2,4-D-injured leaves and berries were examined using light and scanning electron microscopy (SEM). Along with the microscopic examinations, stomatal conductance (gS), leaf growth characteristics, and mineral composition were also determined. The morphoanatomy of healthy leaves resembled that of a typical angiospermic leaf. By contrast, shoots exposed to 2,4-D phytotoxicity displayed epinastic behavior and developed grotesquely malformed leaves that were thick, fan-shaped, enated, and interveinally puckered as a result of fasciation of veins. The cellular architecture, including the vascular bundles, was altered as a result of the formation of parenchymatous replacement tissues. The gS, leaf index, leaf area, and petiole dimensions were significantly reduced in the 2,4-D-injured leaves. 2,4-D-injured leaves; however, accumulated high levels of nitrogen, potassium, and iron compared with healthy leaves. The clusters (fertilized inflorescences) of the injured shoots developed epinastic curvature and predominantly bore live green ovaries (seedless unripened pseudofruit) instead of true berries (fertilized fully ripened fleshy fruit). These abnormalities are expected to severely perturb the vital functions of photosynthesis and transpiration as evidenced by low gS and poor fruit set leading to senescence and localized necrosis ultimately causing death of current-season shoots.

Soil temperature moderates grapevine carbohydrate reserves after bud break and conditions fruit set responses to photoassimilatory stress.

In cultivated grapevines (Vitis vinifera L.), suboptimal photoassimilatory conditions during flowering can lead to inflorescence necrosis and shedding of flowers and young ovaries and, consequently, poor fruit set. However, before this study it was not known whether carbohydrate reserves augment fruit set when concurrent photoassimilation is limited. Carbohydrate reserves are most abundant in grapevine roots and soil temperature moderates their mobilisation. Accordingly, we grew potted Chardonnay grapevines in soil at 15°C (cool) or 26°C (warm) from bud break to the onset of flowering to manipulate root carbohydrate reserve status. Then to induce photoassimilatory responses we subjected the plants to low (94µmolmol-1) CO2 or ambient (336µmolmol-1) CO2 atmospheres during fruit setting. Analyses of photoassimilation and biomass and carbohydrate reserve distribution confirmed that fruit set was limited by concurrent photoassimilation. Furthermore, the availability of current photoassimilates for inflorescence development and fruit set was conditioned by the simultaneous demands for shoot and root growth, as well as the restoration of root carbohydrate reserves. Results indicate that great seasonal variability in grapevine fruit set is a likely response of cultivated grapevines to photoassimilatory stresses, such as shading, defoliation and air temperature and to variations in carbohydrate reserve status before flowering.

METHYL XANTHINE AS A POTENTIAL ALTERNATIVE TO GIBBERELLIC ACID IN ENHANCING FRUIT SET AND QUALITY IN CLEMENTINE CITRUS TREES IN SPAIN

SUMMARYCitrus clementine cv. ‘Nules’ is a seedless mandarin with excellent quality for consumption as fresh fruit; however, its poor fruit set leads to an excess of small-sized fruits. Currently, the only available practice to increase fruit set is the use of the growth regulator gibberellic acid (GA3) as a foliar spray. A trial was conducted to compare an environmentally friendly new bioregulator (MX), containing methyl-xanthine, to GA3 in terms of increasing fruit set and yield of clementine cv. Nules mandarin trees. Fruit yield was significantly increased in treated trees from 17.4 to 25.7% for GA3 and MX treatments, respectively, compared to untreated control trees, without any significant differences between the growth regulators. At the tested doses, MX performed similarly to GA3 in terms of fruit quality and nutrient content, while colour index was not affected significantly by this new bioregulator. A single foliar application of MX was enough to increase fruit set. Spray application of MX on clementine mandarins at the end of the flowering period, when all petals have fallen showed a similar response to GA3 treatments.

Molecular identification of a phytoplasma associated with Ajwain (Trachyspermum ammi) in India

A new disease of Trachyspermum ammi, commonly known as Ajwain in India, was observed in Lucknow, India. The symptoms included small chlorotic leaves, highly proliferating shoots, witches’ broom appearance, shortened internodes and an overall stunted growth. Poor flower heads and fruit setting caused considerable yield losses for farmers. In transmission electron microscopy, pleomorphic bodies were detected in the phloem cells of diseased plants but not in those of healthy plants. The disease etiology was investigated using direct and nested polymerase chain reaction with phytoplasma-specific primers, DNA sequencing, and phylogenetic analysis. Phylogenetic analysis indicated that this phytoplasma clustered in the 16SrVI group. A 1,249 bp sequence (FJ970035) of the 16S rRNA gene from the phytoplasma showed 99% homology with the 16S rRNA gene, (FJ427295) of Ca. Phytoplasma trifolii strain A6 belonging to the phytoplasma group VI (reported from Iran). This is the first report of phytoplasma infection affecting Ajwain (T. ammi).

Development of a Double‐inoculation Method to Assess Resistance to Anthracnose in Trispecies Capsicum Hybrid

AbstractChilli anthracnose is caused by a complex of Colletotrichum species. Breeding for resistance to anthracnose has been focused on introgressing resistance from Capsicum chinense and C. baccatum into commercial C. annuum cultivars. Trispecies hybrids of C. annuum cv. Bangchang, C. chinense PBC932 and C. baccatum PBC80 were successfully produced. Assessments for resistance in F1 progeny to Colletotrichum capsici isolate 158ci (Cc158ci) and C. acutatum isolate MJ5 (CaMJ5) were carried out by inoculating fruit using a laboratory microinjection method. Due to the poor fruit set of the F1 hybrid, a double‐inoculation method was developed to inoculate the same chilli fruit with two isolates of two Colletotrichum species. The positions (apex, centre, end) at which the fruit were inoculated with either isolate did not affect disease development. At 7 days after inoculation, Cc158ci produced larger lesions on chilli fruit than CaMJ5; and lesions from single inoculation were larger than those from double inoculation. The double‐inoculation technique was applied to the trispecies F1 hybrid to select individual F1 plants that contained resistance to both Colletotrichum species. Of the nine F1 plants that produced fruits for inoculation, all were resistant to Cc158ci at both mature green and ripe fruit stages. Two plants were also resistant to CaMJ5 at both fruit maturity stages, and one plant was resistant at the ripe fruit stage but susceptible at the green fruit stage.

Mango diseases in Egypt

Mango diseases in Egypt

Classification of reproductive performance of ten winegrape varieties

Background and Aims: Flowering and fruitset are principal determinants of grapevine yield. Poor fruitset is said to limit the yield of many varieties in most regions in Australia; however, there is a lack of knowledge of the reproductive performance of most varieties under Australian conditions. Methods and Results: The reproductive performance of Vitis vinifera winegrape varieties – Cabernet Sauvignon, Chardonnay, Merlot, Nebbiolo, Pinot Noir, Sangiovese, Sauvignon Blanc, Shiraz, Tempranillo, and Zinfandel – was studied in four consecutive growing seasons (commencing in 2004/05) across a range of climatic regions from cool (Adelaide Hills) to warm (Adelaide Plains). Measures of reproductive performance included flower number per inflorescence, fruitset (%), berry number per bunch, coulure index (CI), and millerandage index (MI). Principal component analysis and agglomerative hierarchical classification were used to group the varieties into three classes of reproductive performance. Conclusions: Certain varieties have a reputation of having ‘poor fruitset’ that has been inferred from relatively low berry number per bunch; however, for some of these varieties, it is ‘low flower number per inflorescence’ rather than ‘poor fruitset’ that is the cause of low berry number. Significance of the Study: An improved understanding of the reproductive performance of winegrape varieties has been achieved.

First report of Pyrenochaeta lycopersici, causal agent of tomato corky root rot in Australia

Corky root rot, chlorosis of foliage, necrosis of tip branches and poor fruit setting were observed in field and glasshouse tomatoes (Lycopersicon esculentum L.) grown north of Perth during the summer of 2008. Based on morphological characteristics of the isolated fungus, disease symptoms and a pathogenicity test, Pyrenochaeta lycopersici was identified as the causal agent of corky root rot of tomato. Pyrenochaeta lycopersici has not previously been reported on tomato in Australia.

Scoring and Girdling, but not GA3, Increase Yield without Decreasing Return Bloom in ‘Triumph’ Persimmon

The persimmon (Diospyros kaki Thunb.) cultivar Triumph is prone to poor fruit set, particularly in young orchards, in both Israel and South Africa where it is mostly grown. Two applications of 20 mg·L−1 gibberellic acid (GA3) at 30% and 70% full bloom (FB) are recommended as the industry norm to increase fruit set, but results obtained are often unsatisfactory. We conducted experiments during the 2005–06 and 2006–07 seasons in a young orchard (less than 5 years old) and a full-bearing orchard to determine the efficacy of GA3 application and scoring or girdling during FB to increase fruit set and yield in ‘Triumph’ persimmon. We also established the effect of 2005–06 treatments on return bloom in 2006–07. Although GA3 treatments were ineffective in increasing fruit set and reduced cumulative yield over the two seasons as a result of a reduction in return bloom, scoring increased the cumulative yield by 50% compared with the untreated control and by 92% compared with GA3 application in the young orchard. In the full-bearing orchard, scoring or girdling increased the cumulative yield over the 2005–06 and 2006–07 seasons by 52% compared with the industry standard GA3 application and by 22% compared with trees that received scoring/girdling in addition to GA3. Hence, scoring or girdling did not entirely offset the negative effect of GA3 application on return bloom. The increase in fruit numbers in response to fruit set treatment brought about a reduction in fruit mass. In conclusion, the ineffectiveness of GA3 in increasing fruit set and its negative effect on return bloom do not justify its further use to improve fruit set in young or full-bearing ‘Triumph’ orchards in South Africa. Either scoring or girdling can be used to increase yield but will need to be accompanied by pruning and thinning strategies to achieve adequate fruit size and to prevent the onset of alternate bearing resulting from overcropping.

Observations on the morphology and development of star flowers ofVitis viniferaL. cvs Chardonnay and Shiraz

Background and Aims: Following our original discovery of star flowers on grapevines in Australia, further variants of the star flower phenotype have been discovered on other varieties in South Australia. The objective of this report was to describe star flowers on Vitis vinifera L. cvs Chardonnay and Shiraz. Methods and Results: Field and microscopic observations revealed that star flowers on both varieties opened precociously; there was neither pollen nor pollen tubes on the stigmas of the star flowers, and both Chardonnay and Shiraz star flowers contained aberrant ovules. The Chardonnay vines with star flowers produced bunches with an abundance of seedless berries; however, star flowers on Shiraz vines did not develop into berries. Conclusions: The inability of the Shiraz star flowers to develop into berries suggests that either there are two different mutations affecting these two varieties, or else the difference lies in their contrasting parthenocarpic tendencies. Significance of the Study: The star flower variants described here and previously may be the result of deviations to the normal molecular pathway for flower development in Vitis species. The identification of star flowers on numerous varieties and in several different regions suggests that the occurrence of star flowers may be more widespread than previously realised, and the association of star flowers with the production of seedless berries and poor fruitset suggests that star flowers may also play a significant role in the problem of poor fruitset.

Influences of Cross Pollination on Pollen Tube Growth and Fruit Set in Zuili Plums (Prunus salicina)

Zuili plum (Prunus salicina L.) trees usually set fruit poorly, although they produce high quality fruit. To elucidate the causes of the poor fruit set, pollen tube growth into pistils and fruit set percentage were investigated after cross-, self- and open-pollination. Ovule development in Zuili pistils was also investigated. Pollen tube penetration into the ovules via the obturator and micropyle was best when Zuili pistils were pollinated by cv. Black Amber (P. domestica) pollen grains, although cross-pollinations with Hongxinli and Miili (P. salicina) pollen were more effective than self- and open-pollination. The fruit set percentage was also highest in pistils pollinated with Black Amber pollen grains. Morphological observation of Zuili pistils revealed that the trees produce "double pistils", developing two ovaries from a basal pistil, at a rate as high as 28%. In such abnormal pistils, most ovules were lacking an embryo sac or were entirely degenerated. The percentage of normally developed ovules was 24.3% and 8.9% in normal and double pistils, respectively. From these results, we conclude that the main causes of poor fruit set of Zuili plums are a lack of effective cross-pollination and the production of high percentages of double pistils in which normally developed ovules are scarcely formed.

ON-FARM ASSESSMENT OF CONSTRAINTS TO CHICKPEA (CICER ARIETINUM) PRODUCTION IN MARGINAL AREAS OF NORTHERN AUSTRALIA

Chickpea production in marginal (<600 mm annual rainfall) areas of the northern cropping region in eastern Australia is considered to be constrained by low rainfall, soils with low plant available water capacity (PAWC), subsoil salinity, low plant stature and poor fruit set. This study examines these constraints to assess the magnitude of their impact and if agronomic practices can improve potential production. Over three years a total of 42 commercial chickpea crops were monitored following a participatory action research approach focusing on perceived production constraints. Subsoil salinity significantly reduced PAWC for chickpea compared to wheat. However, PAWC for chickpeas from the majority of sites monitored was comparable to other areas. The supply of water between flowering and maturity was significantly related to yield. The agronomic practice of levelling following deep planting improved the lowest pod height by 10 cm and plant stresses experienced during flowering caused a 50 % loss of potential fruit. Constraints impacting on the supply and storage of soil water could be minimized by selecting paddocks with low chloride levels in the upper layers and sowing crops when the available soil water is greater than 100 mm. Reducing fruit loss at flowering has the potential to improve yields significantly. The mechanisms behind this loss were not identified but are worthy of further research.

PLANT EXPLORATION FOR FRUIT GENETIC RESOURCES IN SAKHALIN TERRITORY

ISHS XXVII International Horticultural Congress - IHC2006: II International Symposium on Plant Genetic Resources of Horticultural Crops PLANT EXPLORATION FOR FRUIT GENETIC RESOURCES IN SAKHALIN TERRITORY

Natural occurrence of autopolyploidy within the allotetraploid-cultivated peanut

The cultivated peanut is classified as an allotetraploid species. During the past several years, abnormal plants with coarse stems, thick leaves and an occasional single seed per pod have been found within different cultivars and advanced breeding lines. The spontaneous natural occurrence of these plants has been very rare, and frequently they do not produce any pods or seed. However, over a 3-year period (2001–2003), four individual plant selections with one mature seed per plant were found and saved. In 2003, another similar plant was also found that had the same plant characteristics, except for a single branch that had normal leaves with typical two-seeded pods. A greenhouse study was conducted during the winter of 2003–2004. The four coarse stem individual plant selections from the previous years were planted along with the check cultivar ‘Georgia Green’ and the sectorial plant found in 2003. S1 seed from both the one-seeded pods as well as normal two-seeded pods were planted from the sectorial plant. Relative DNA content was measured by flow cytometry on all plants. Results from the test showed that the coarse stem, thick leaf plants with poor fruit set were autooctoploids and had about twice the DNA content when compared with the normal sectorial branch and the allotetraploid peanut cultigen.

Influence of propagation techniques on growth and yield of olive trees cultivars ‘Carolea’ and ‘Nocellara Etnea’

Abstract The vegetative and productive performance of micro-propagated olive plants in comparison with grafted and own-rooted plants was evaluated in southern Italy. Two cultivars of Olea europaea L. ‘Carolea’ and ‘Nocellara Etnea’, were planted in 1997 at two-row spacings: 6 m × 3 m and 6 m × 6 m. Percentage of flower bud differentiation, fruit weight, yield, pruning material and trunk diameter were measured on each plant of the experimental plot. Plants came into flowering the second year after planting with significant differences between cultivars. Micro-propagated ‘Nocellara Etnea’ plants came into bearing as early as the second year, whereas grafted plants had no bearing. Eight years after planting, cumulated yield of ‘Nocellara Etnea’ plants was almost double as compared to the ‘Carolea’ plants. Yield from micro-propagated plants was slightly higher with respect to grafted plants in ‘Nocellara Etnea’, but fruit weight was significantly lower. Micro-propagated ‘Carolea’ plants have shown a similar percentage of flower buds but a very low cumulated yield in the period of the trial, due to poor fruit set. In general, vegetative growth was significantly higher on plants with lower crop level. Our results have shown that micro-propagated plants did not exhibit any juvenile trait as, for instance, delay in flowering. In vitro propagation can thus be a rapid and a powerful olive propagation technique. Further investigations are however necessary to check if the main phenological differences observed (average fruit weight and poor fruit set) are somehow due to genetic modifications induced by in vitro propagation.

Transport of Cross-pollen by Bumblebees in a Rabbiteye Blueberry Planting

Rabbiteye blueberry (Vaccinium ashei Reade) is a bee-pollinated small fruit crop that often exhibits poor fruit set. Mixed cultivar plantings are recommended because cross-pollination is required for optimum yields, and bees are expected to transfer pollen from one cultivar to another. The objective of this study was to assess transport of cross-pollen by bumblebees in a rabbiteye blueberry planting. Experiments were conducted in 2003 and 2004 in a plot composed of `Brightwell' and `Climax' plants arranged in alternating rows. The proportion of `Brightwell' and `Climax' pollen carried on the bodies of bumblebees was estimated based on frequency distributions of pollen diameter, measured with a particle counter. About 75% of bumblebees collected in 2003 carried <20% cross-pollen. Proportions of cross-pollen in 2004 were higher than in 2003, but still, about 85% of bumblebees collected carried <40% cross-pollen. The proportion of cross-pollen carried by bumblebees changed during the flowering season. The greatest likelihood for cross-pollination occurred during the time of maximum bloom overlap, although the median proportion of cross-pollen was not >30% on any sampling day of 2004. The results from this study emphasize the need to select more self-fertile rabbiteye blueberry cultivars and to maximize bloom overlap in blueberry plantings.

INFLUENCE OF PLANT SIZE AND CLIMATIC VARIABILITY ON THE FLORAL BIOLOGY OF FOUQUIERIA SPLENDENS (OCOTILLO)

The floral biology of Fouquieria splendens (Fouquieriaceae), a drought-deciduous shrub with wandlike branches, was studied in the northern Sonoran Desert. Two different measures of plant size, number of branches long enough to flower (>1 m in length) and actual number of reproductive branches, were used to examine the effect of plant size on reproductive output and floral display. Number of flowers and fruits increased with either measure of plant size. Annual flower production ranged from 190 to 6465 per plant and averaged 2553. Annual fruit production ranged from 9 to 1760 per plant and averaged 390. Because some branches long enough to flower did not do so, number of reproductive branches was a stronger predictor of flower production than number of branches > 1 m long. Inflorescence size (mean number of flowers per panicle) was not significantly related to plant size (number of flowering branches) in 2002 or 2003; in fact, the range in inflorescence size on certain individual plants was about as wide as the range for the entire sample. Interannual variation in floral parameters was examined by monitoring the same set of branches in two years, one unusually dry, one with nearly normal rain. In 2002, the dry year, panicles were numerous and sparsely flowered; in 2003, the wetter year, panicles were relatively few and much more densely flowered. Although flowers appeared normally abundant in the wetter year, mean number of flowers per branch was in fact 39% lower than in the dry year. Percent fruit set per panicle in 2003 (36%) was more than twice that in 2002 (16%). Even so, average number of fruits per branch did not differ between 2002 and 2003. Evidently flower production on a per-branch basis was high enough in 2002 to compensate for poor fruit set in that year, resulting in about as many fruits as in 2003.

POLLEN DISPERSION IN RABBITEYE BLUEBERRY

Poor fruit set is one of the most important horticultural problems of the rabbiteye blueberry industry. Rabbiteye blueberries require cross-pollination and several bee species are expected to transfer pollen from one cultivar to another. A novel method was developed to measure bee-mediated pollen dispersion in rabbiteye blueberry. Pollen diameters were used to predict the proportion of cross-pollen in bumble bees' pollen load. Bumble bees visiting blueberry flowers had low proportions of cross-pollen. It is proposed that inadequate levels of cross-pollination play a major role in the failure of rabbiteye blueberries to set adequate commercial crops. The composition of bees' pollen load changed with the phenology of the crop. Data indicate that the greatest likelihood for cross-pollination occurred around the time of maximum bloom overlap of the two studied cultivars.

Effects of CPPU on Fruit Size, Set, and Yield of Southern Highbush Blueberry in Florida

Poor fruit set and sub-optimum berry size are potential yield- and profit-limiting factors for southern highbush (Vaccinium corymbosum) blueberry production in Florida. The cytokinin N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU) has increased fruit size and fruit set of a number of fruit crops including rabbiteye blueberry. The purpose of this study was to determine the effects of CPPU applied at different rates and phenological stages of bloom and/or fruit development on fruit size, set, and yield of southern highbush blueberry. `Millennia' and `Star' southern highbush blueberry plants located on a commercial blueberry farm in Alachua County, Fla., were treated with 5 or 10 ppm CPPU at various stages of development ranging from full bloom to 20 days after full bloom. In contrast to findings with rabbiteye blueberry, fruit set in this study of southern highbush blueberry was not affected by any of the CPPU treatments when compared to the controls. Nor was total fruit yield affected by CPPU treatments. The most noticeable potential benefit found in this study was an increase in mean fruit fresh weight from CPPU treatments. However, cultivars responded differently to CPPU with respect to mean fruit fresh weight. For `Millennia', only one CPPU treatment increased mean fruit weight compared to controls. However, for `Star', all but one CPPU treatment increased mean fruit fresh weight. Several CPPU treatments resulted in delayed fruit ripening for `Star' but not for `Millennia'. For `Star', the treatments that most consistently delayed fruit ripening tended to have greater fruit fresh weights.

The Effective Pollination Period in Rabbiteye Blueberry

Rabbiteye blueberries (Vaccinium ashei Reade) often exhibit poor fruit set under commercial field conditions. Problems of low fruit set have been attributed to short periods of flower receptivity in different fruit crops. This study seeks to establish the effective pollination period (EPP, defined as the number of days during which pollination is effective to produce a fruit) in rabbiteye blueberry. The cultivars Brightwell and Tifblue were chosen due to their known difference in fruit set and field performance. Flowers were hand pollinated 0, 2, 4, 6, and 8 days after anthesis (DAA) using self- and cross-pollen. Fruit set, seeds per berry, berry weight and days to ripening were recorded. Fruit set showed a polynomial trend across flower ages. `Brightwell' was highly receptive from the day of anthesis, whereas, `Tifblue' receptivity was low until 2 DAA. `Brightwell' and `Tifblue' flowers produced adequate fruit set (≥50%) over a period of 7 and 5 days, respectively. In `Tifblue', fruit set was limited by the low receptivity of newly opened flowers. The difference in EPP helps to explain the performance of these cultivars in the field. The rate of ripening increased with flower age in both cultivars. The number of seeds per berry was affected by flower age only in `Tifblue'. The effect of flower age on berry weight depended on the cultivar and the pollen source.