Flower emasculation accelerates ovule degeneration and reduces fruit set in sweet cherry

Flower emasculation is commonly used to make flowers unattractive to pollinating insects and to carry out controlled pollinations. In sweet cherry, we have observed recurrent low fruit set after flower emasculation and compatible pollination without apparent causes. This led us to evaluate its effect on the progress of the reproductive phase and on fruit set in this species. Flower emasculation reduced by more than a half the fruit set obtained in crosses made during two consecutive years. This effect could be traced back to the first week after anthesis where weight increase of pistils from emasculated flowers was smaller and ovule degeneration was accelerated compared to pistils from non-emasculated flowers. Pollen tubes, which behaved similarly at the stigma-style level in emasculated and non-emasculated flowers, lost their directionality in the area close to the degenerated ovule in the ovary. While flower emasculation is valid to evaluate pollen tube performance in the style and to determine incompatibility relationships, the lower fruit set registered after emasculation alerts on its use in fruit set experiments and breeding programs.     

Self-fertilization in homozygous and heterozygous self-compatible almonds

In homozygous self-compatible genotypes 100% of the pollen grains are potentially able to grow through their own pistil, and thus the rate of self-fertilization could be higher than in heterozygous self-compatible genotypes. To evaluate the advantages of growing homozygous self-compatible almonds, pollen tube growth along the pistil at different times following self-pollination, and fruit set were studied in four homozygous and four heterozygous self-compatible seedlings. The results showed important differences between homozygous and heterozygous individuals for the percentages of pollen tubes in the third section of the style at 24 and 48 h, the pollen tube growth rate being higher in the homozygous. Twenty-four hours following self-pollination only the homozygous individuals showed pollen tubes in the ovary. However, at 72 and 96 h those values were similar for both genotypes, suggesting that space and availability of nutrients become the main limiting factors, overcoming the genetic interactions between pollen and pistil. In general, fruit set was similar in homozygous and heterozygous individuals. Interestingly, one of the homozygous individuals showed problems of fruit development, which might be explained by its inbred origin.     

Molecular and physiological identification of new S-alleles associated with self-(in)compatibility in local Spanish almond cultivars

The S-allele characterisation of ‘Alzina’ and ‘Garondès’, two local almond cultivars from the island of Majorca, by a multidimensional approach has allowed the confirmation of the presence of the S_f-allele and the identification of a new allele not previously described in almond, S₃₆. When these cultivars were phenotypically evaluated, both showed a self-incompatible phenotype and were cross-incompatible, as assessed by artificial self- and cross-pollinations and fruit sets after field pollinations, confirming that their S_f-allele is in its active form, S_fa. Thus a new CGI group in almond is proposed and named XXVIII. These results confirm the wide diversity of S-alleles in almond both at genotypic and phenotypic levels, as well as their similarity with the S-alleles from other close Prunus species. This similarity suggests the possibility of allele introgression between species or allele identity by descent from a common ancestor.     

Rain effect on pollen–stigma adhesion and fertilization in almond

The fact that rainy weather negatively affects production in almond is well-known by growers. However, as far as we know, no previous study has been carried out in this species to determine if the rain is able to wash off pollen grains from the stigma surface and consequently affect fertilization efficiency. To answer this question, flowers of the self-compatible almond cultivar ‘Antoñeta’ were emasculated on branches of trees in the field, pollinated by hand with pollen of the cultivar ‘Marcona’, and sprayed with water to simulate the rain effect at 4, 8, 24 and 48 h after pollination. A control for which no treatment was applied was also included in the assay. Seven days after spraying the flowers, the number of germinated pollen grains on the stigma was recorded in 10 pistils for each treatment by fluorescent microscopic observation. In addition, for each treatment the initial and final fruit set were determined at 30 and 60 days after pollination, respectively. The following year additional assays were performed in the field and in the laboratory in order to complete the study with earlier treatment times. Thus, an assay of rain simulation in the field at 0 and 2 h, and other consisting on immersing a branch with flowers and shaking it in a water container in the laboratory at 0, 30, 60 and 120 min after pollination were performed. One sample more was immersed, shaken, then pollinated and again immersed and shaken. The results from field assays showed that adhesion of pollen grains to the stigma was very quick and strong, and the treatments did not significantly affect pollen–stigma adhesion and subsequent fruit set. On the other hand, laboratory results showed that all washing treatments decreased the number of germinated pollen grains on the stigma, mainly when the flowers were immersed before pollination. In conclusion, the results showed that the simulated rain was not able to completely wash off pollen grains from the stigma surface, although it seems to affect adhesion in forthcoming pollinations.     

梨不同花龄自花与异花授粉的花柱内花粉管生长及坐果率的比较

对自交不亲和强度不同的梨品种丰水和菊水的不同花龄花进行自花授粉和丰水×菊水异花授粉后,用荧光显微镜观察花粉萌发及生长特性。结果表明,开花当天及以后的自花和异花授粉花粉在柱头上均有较高的萌发率;自花和异花花粉管在花柱内的生长速度及停止生长的位置不同,丰水自花授粉后花粉管生长的短且慢,菊水自花花粉管生长的长且快,而异花授粉的花粉管生长最快。自花授粉后,不同花龄对花粉管生长影响表现为:开花4d前的蕾期授粉以及开花4d后的延迟授粉,花粉管生长长度显著的长。开花6d前的各种授粉组合,花粉管生长均较差。这与田间授粉坐果率的高低基本一致,即整体表现为各个花龄的授粉都以异花授粉坐果率最高,其次为菊水自花授粉,丰水自花授粉坐果率最低。另外,自花授粉中,蕾期授粉和延迟授粉(开花2d后除外)坐果率都有提高,而异花授粉中蕾期授粉和延迟授粉的坐果率却有所下降。     

精胺对梨花粉原位萌发及花粉管生长的影响

为进一步研究活体条件下精胺对梨花粉萌发及花粉管生长的影响,以幸水、新雪、长-二十世纪为材料,采用荧光显微镜观测了不同浓度精胺处理的花粉萌发及花粉管生长情况。试验结果表明:较低浓度的精胺能促进花粉萌发,而超过一定浓度时则表现抑制作用,适宜于花粉萌发的精胺浓度是0-0.025mmol/L。精胺对花粉管生长的促进作用因品种而异,0-0.05mmol/L,精胺促进幸水、新雪花粉管生长的作用主要表现在花柱中上部;而到达基部的花粉管仍较少,与对照间差异不显著。在0-0.025mmol/L的适宜浓度下,精胺可促进长-二十世纪花粉管生长并到达花柱基部。不同浓度的精胺对幸水、新雪坐果影响不大;而适宜浓度的精胺可促进长-二十世纪坐果。     

Influence of genotype,year and type of fruiting branches on the productive behaviour of almond

The effect of the type of fruiting branch was studied over 2 years in nine almond selections in order to investigate its relationship with bloom density, fruit set, the level of the subsequent crop, and the physical traits of the fruits. The effect of the fruiting branch, defined by the presence of spurs, was found to be highly significant for bloom density, productivity and fruit size, but not for fruit shape, showing that nut and kernel shapes are cultivar traits. Bloom density and its components, as well as fruit set, fruit density and productivity were highly genotype and year dependent, but the interaction genotype × year was less important or even non-significant, stressing the special behaviour of each genotype as well as the effect of the year, probably linked to the climatic conditions and to the physiological status of the trees.     

The almond Sf haplotype shows a double expression despite its comprehensive genetic identity

Since self-compatibility has become the primary objective of most almond breeding programmes, search for new self-compatibility sources has acquired a great importance in almond research. The local Spanish cultivar ‘Vivot’, identified as showing the genotype S₂₃S_f, thus presumably self-compatible, was found to be unexpectedly self-incompatible in spite of the presence of the S_f allele, as also observed in other almond cultivars. However, not only the coding sequences of both the S_f-RNase and the SFB_f of ‘Vivot’ and ‘Blanquerna’, a confirmed self-compatible cultivar, were identical, but also the 5′ regulatory sequence of the S_f-RNase of both. Thus, the reason for the different expression of the S_f is independent of the complete genetic identity found in the whole chromosome region bordering the S-locus in the almond cultivars sharing the S_f allele.     

Fruit quality parameters of ‘Pioneer’ Japanese plums produced on eight different rootstocks

The influence of Marianna GF 8-1, GF 677, Julior-Ferdor, Nemared, Monegro (G × N 9), Felinem (G × N 22), Adesoto 101 and Cadaman rootstocks on fruit quality of ‘Pioneer’ Japanese plum was analysed. The study was performed during three consecutive years in the Guadalquivir Valley (Seville, Spain), on a silt loam and calcareous soil. Colour, fruit size, fruit and stone weights, hardness, soluble solid concentration and acidity were measured for fruit quality evaluation. In general, the effect of the different rootstocks on most of the analysed quality parameters was variable because a strong interaction rootstock × year was observed. However, several parameters as fruit shape, soluble solid concentration, acidity and maturity seem to be harder conditioned in some rootstocks, did not show significant differences year-by-year. Fruits produced on scions grafted on Marianna and Nemared showed the highest soluble solid concentration and Cadaman the lowest, the last also originated the hardest fruits and the lowest maturity.     

Correlations between quantitative tree and fruit almond traits and their implications for breeding

Correlations between 29 quantitative tree and fruit traits were studied in 46 almond genotypes and some inter-specific crosses. Results reflected a significant diversity in the assayed almond germplasm. In addition, the obtained cluster demonstrated varying degrees of relationships, illustrating higher correlation values for the flowering traits and lower correlation values for the nut and kernel traits. To determine the importance of the traits and the levels of similarity existing between the various studied traits, a discriminate analysis was carried out. According to the results obtained from these analyses, the different traits were discriminated on basis of the characteristics of the presence of double kernels, the nut and the kernel size, the flowering date, kernel yield and shelling percentage. Finally, this study evidenced correlations between most of the agronomic traits in almond, although the correlations coefficient (r) value was found to be higher than 0.5 only in some cases. This analysis can help breeders for choosing the most favorable entries to build a core subset of the almond collection for the purpose of breeding.     

Effects of shading and thidiazuron + oil treatment on dormancy breaking,blooming and fruit set in apricot in a warm-winter climate

Overcoming dormancy represents one of the major limitations to fruit tree production in warm areas. High temperatures during the chilling period have a negative effect on breaking of dormancy. Shading of trees reduces the incidence of radiation and the temperature. Previous works on shading did not take into account the stage of dormancy. The aim of this work was to evaluate the effects of shading during different periods of endodormancy, in an area having relatively warm winters, and the effects of a treatment of thidiazuron ([TDZ] N-phenyl-N-1,2,3-thiodiazol-5-il-urea) and winter oil, on apricot blooming, fruit set and ripening. The study was carried out during three years which showed marked differences regarding chilling accumulation. Autumn shading did not affect blooming or harvesting. Regarding harvest date, 2–3 days of precocity were achieved by shading during endodormancy, relative to the control. The TDZ + oil treatment increased blooming percentage, made blooming more uniform and brought forward the blooming (by 7–14 days) and ripening (3–8 days) dates. However, pistil abortion percentage was strongly increased by using TDZ and winter oil when there was low chilling accumulation, which led to reduce fruit set percentage. Shading during late endodormancy produced 5 days precocity for the harvest date in the year with lower chill accumulation. Shading of trees during endodormancy and TDZ + oil treatment could be suitable for increasing precocity in warm-winter climates. Significant year-to-year variation has been shown for blooming, pistil abortion, fruit set and fruit/bud percentages. Correlations among these variables are also discussed. Under conditions of marginal chill accumulation, the distribution of chilling during autumn and winter had an important role in the overcoming of dormancy, blooming and fruit set.     

Mitigation of severe water stress by fruit thinning in ‘O’Henry’ peach: Implications for fruit quality

Fruit thinning can be used to relieve water stress in peach but it is not known how fruit quality will respond under water limited conditions. To elucidate this, we applied, over the growing seasons of 2003 and 2004, irrigation and fruit thinning treatments to ‘O’Henry’ peach at the onset of Stage III of fruit development. The treatments were full irrigation (FI) and no irrigation (NI) with each receiving three crop load levels: light, commercial and heavy. Fruit size and fruit skin colouration were lower in NI than in FI but the following were higher in NI fruit: firmness, juice titratable acidity and electrical conductivity, and concentrations of dry matter and soluble solids. All the quality parameters were significantly correlated with tree water status, expressed as midday stem water potential. NI fruit matured 5–10 days later than FI fruit. The increased dry matter concentration, juice acidity, and electrical conductivity in NI fruit were indicative of lower quality at harvest. Choosing a light crop load was not effective in improving NI fruit quality except for the size. Since fruit size is the most important fruit quality attribute, its increase might compensate for yield losses resulting from heavy fruit thinning. Nevertheless, when heavy thinning is performed for mitigation of water stress in Stage III, the overall fruit quality will suffer if severe water stress is inevitable because of shortage or lack of irrigation water.     

Fruit and seed diversity of domesticated carob (Ceratonia siliqua L.) in Morocco

The carob tree (Ceratonia siliqua L.) is an important economic resource for Morocco's rural populations. This species is used in reforestation actions and its cultivation in modern orchards is being undertaken to valorize marginal lands and substitute for drought sensitive species. However, little data is available on its intra-specific variability and its adaptability. Morphological characters of pods and seeds from 13 ecoregions of private-domesticated carob were used to assess phenotypic variation of this species. These stands extend from south-west to north-east and cover a wide range of Morocco's ecoregions. Pods length, width, thickness, seeds number, pulp weight, seeds yield and seeds length, width, thickness and weight were measured for 390 trees (30 trees per ecoregion). Statistically significant differences were found between ecoregions for all characters which were examined, what indicates a high phenotypic diversity. Principal component analysis (PCA) and hierarchical cluster of all ecoregions lead to identify two major and opposite groups (the northern ecoregions; and the central and south-western ecoregions). Ecoregions of the north of Morocco exhibited the largest and the thickest pods with the highest pulp weight while other ecoregions have relatively short pods but largest proportion of seed yield. Similarly, the northern ecoregions are characterized by the heaviest seeds. A correlation matrix between morphological characters, geographic parameters and precipitation exhibits a positive and a negative correlation of pods thickness and pulp weight with the latitude and the altitude, respectively. Seed yield and weight are negatively and positively correlated to pod width, pod thickness and pulp weight, respectively. In addition, seed weight is positively correlated with the latitude. The geographic pattern of the carob tree and its variability are discussed in this paper.     

Fruit weight is related to ovary weight in olive (Olea europaea L.)

Fruit size is an important parameter both for scientific understanding and for commercial purposes. In many species, mature fruit size is often related to floral ovary size, but no literature exists in olive that demonstrates such a relationship. Previous work suggests that olive cultivars with different fruit sizes have similar cell number and size in the ovary transectional area, but ovary and fruit dry weight was not measured. In the present study, ovary dry weight and fruit dry weight during the whole fruit development season until harvest were measured in olive cultivars with different fruit size, over three years. Flower dry weight was also measured. Fruit weight at harvest was strongly correlated to ovary weight at bloom, both in single-year data and when data from three years were pooled. Flower dry weight, excluding the ovary, was also correlated to ovary dry weight. Ovary dry weight was strongly correlated not only to the fruit dry weight at maturity, but also at any date during fruit development. The mature fruit/ovary dry weight ratio ranged between 1000 and 4000 among cultivars, but was not correlated to the fruit dry weight at maturity. These results suggest that, in olive, fruit weight is genetically controlled through the ovary weight at bloom. This knowledge may have implications in the understanding of fruit set and source-sink relationships in olive.     

Relation of carbohydrate reserves with the forthcoming crop,flower formation and photosynthetic rate,in the alternate bearing ‘Salustiana’ sweet orange (Citrus sinensis L.)

The aim of this work was to assess the relation between carbohydrate levels and flower and fruit production, as well as the role of carbohydrates on CO₂ fixation activity, by analysis of leaves, twigs and roots from the alternate bearing ‘Salustiana’ cultivar of sweet orange (Citrus sinensis [L.] Osbeck). A heavy crop load (on year) did not affect photosynthesis activity when compared to non-fruiting trees (off year). Fruiting trees accumulated most of the fixed carbon in mature fruits, whilst no accumulation was observed in roots before harvest. Non-fruiting trees transported part of the fixed carbon to the roots and mobilize it for growth processes and, at the end of the season (December), store it as reserves. Reserve carbohydrates accumulation in leaves started by early December for both tree types, showing the same levels in on and off trees until spring bud sprouting. A heavy flowering after an off year caused the rapid mobilization of the stored reserves, which were exhausted at full bloom. We found no evidence on carbon fixation regulation by either fruit demand or carbohydrate levels in leaves. Carbohydrate reserves played little or no role over fruit set, which actually relied on current photosynthesis.     

Fruit set is inversely related to flower and fruit weight in olive (Olea europaea L.)

Fruit weight is strongly correlated to ovary weight in olive as big-fruited cultivars have larger ovaries and flowers at bloom. We tested the hypothesis that larger ovaries imply stronger sinks and therefore reduce fruit set, expressed as number of fruits. Flower/fruit load per centimeter of shoot was assessed every month from flowering to harvest, on sample shoots of many different olive cultivars differing in fruit size. Data were taken for two years: 2007 and 2008. Additionally, in 2008, a fruit thinning experiment was carried out by leaving a single fruit per shoot, to assess the maximum potential fruit weight achievable by each cultivar. Results indicated that fruit size was mostly genetically determined as thinned fruits of small-fruited cultivars, although bigger than control fruits, never got as big as fruits from large-fruited cultivars, confirming that large ovaries are a prerequisite for large fruits. Among all cultivars, the number of flowers per inflorescence, the number of inflorescences, and the number of flowers per centimeter of shoot were not correlated to average flower weight while total flower mass per centimeter of shoot was positively correlated to average flower weight (i.e. large flowered/fruited cultivars had greater total flower mass). However, one month after bloom and thereafter, all parameters were negatively and exponentially correlated with fruit average weight across cultivars, except fruit mass per centimeter of shoot which was generally not correlated to fruit average weight, except in one year, at harvest, when fruit mass per centimeter of shoot was positively correlated to fruit average weight. These results suggest that fruit set is a consequence of, and inversely proportional to flower/fruit size in olive.     

Study of long-distance movement of Plum pox virus (Sharka) as an alternative resistance-evaluation method in Prunus

During the breeding programs for Plum pox virus (PPV, Sharka) resistance in Prunus, the evaluation of the new releases through symptoms observation on leaves has been contradictory and represents one of the main handicaps in these programs. In order to increase the accuracy of this traditional evaluation method, we here analyze an alternative method based on the study of the ability of a genotype to allow the long-distance movement of the virus through its vascular vessels. Two different plant models have been assayed: (a) in Model I, the inoculation was performed in the ‘GF305’ rootstock with a later grafting of the genotype under evaluation and a scion of healthy control ‘GF305’, to evaluate the long-distance movement through the studied genotype from the rootstock to the scion (xylem transport), and (b) in Model II, the inoculation with ‘GF305’ diseased scions was performed by grafting these diseased scions onto the studied genotypes, which were grafted onto healthy ‘GF305’ peach seedlings, to evaluate the long-distance movement through the studied genotype from the scion to the rootstock (phloem transport). The results show that, regardless of the presence of symptoms, susceptible genotypes allowed the movement of the virus through their vascular vessels in both directions studied. However, the resistant apricot ‘Stark Early Orange’ did not allow this movement. We propose the study of the ability of a genotype to allow the long-distance movement of the virus as an alternative and more accurate method for the evaluation of PPV resistance. However, this protocol is much more tedious than the traditional one and could be used mainly in the evaluation of a reduced number of more interesting genotypes.     

Uniconazole is an effective blossom thinner for ‘Bing’ cherry (Prunus avium)

Small fruit size is one of the limiting factors in marketing cherries (Prunus avium L.). Several techniques have been used to improve fruit size; among them, blossom and fruit thinning in order to reduce crop load have proved effective. Unfortunately, hand thinning is very costly, and chemical thinning has proved ineffective. In the present study, carried out in two consecutive years (2006–2007), application of uniconazole (E-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl-1-penten-3-ol)) at 100–125 mg l⁻¹, in the form of 0.2–0.25% Magic™, at 30% full bloom, reduced the fruit set of ‘Bing’ cherry fruit. As a result time spent in hand thinning was reduced by about 50% and the crop load by about 40%, and there was a considerable shift to larger fruit size (>26 mm), provided the crop load was not too low. No negative effects were observed on the return bloom and yield in the following year.     

The effects of temperature on in vitro pollen germination and pollen tube growth of Pistacia spp.

The pollen germination and pollen tube growth among nine Pistacia genotypes was quantified in order to identify differences in the tolerance of pollen to temperature variations. The effect of temperature on in vitro pollen germination and pollen tube growth was investigated in Pistacia vera (Uygur, Atli, Kaska, Sengel, Kavak), P. atlantica, P. khinjuk, P. terebinthus and P. palaestina. When pollen was incubated in a germination medium for 24 h in darkness, distinct differences were observed in pollen germination and pollen tube growth at different temperatures.     

Combining endophytic fungi and bacteria for the biocontrol of Radopholus similis (Cobb) Thorne and for effects on plant growth

Eight endophytic fungal and bacterial isolates with antagonistic activity against Radopholus similis were evaluated in vivo for their individual and combined effects on biocontrol of R. similis and on the growth of “Grand Naine” cultivar banana plantlets in the greenhouse. Penetration efficiency (PE) of R. similis was between 3 and 21% in 29 biological agents (BAs) treatments, less than the 29% of the nematode-alone control (p ≤ 0.0001); 24 of the BAs treatments did not differ from the PE of 5% for a nematicide control. Twenty nine BAs treatments exhibited antagonistic activity against nematodes which reduced final population levels between 18 and 93%, relative to those on nematode-alone control plants (p ≤ 0.0001), and 14 BAs treatments were statistically similar to the nematicide treatment (88% reduction). Twenty four BAs treatments had increments of plant root biomass ranging from 20 to 58%, greater than the control plants; 37% of the treatments with single and combined BAs inoculations had root length increments ranging from 29 to 54% compared with control and chemical treatment. The nematicide, Terbufos 10GR, did not affect plant growth.