Effect of ethephon on sweet cherry pedicel-fruit retention force and quality is cultivar dependent

Ethephon (2-chloroethyl phosphonic acid) is effectively used to promote development of the pedicel-fruit abscission zone in tart cherry (Prunus cerasus) for mechanical harvest. Our research program is investigating the use of ethephon to promote pedicel-fruit retention force (PFRF) reduction on new sweet cherry (P. avium) cultivars to assist mechanized harvest and its affect upon fresh market quality fruit. Ethephon treatments were made at different timings and rates to ‘Bing’ and ‘Chelan’ during the 2006 season. Ethephon applications to ‘Bing’ trees more than 10 days prior to harvest were effective at reducing PFRF and facilitating mechanical harvest, irrespective of rate (1.2, 3.5, 5.8 L ha⁻¹ [1, 3, 5 pt A⁻¹]). Ethephon applied fewer than 10 days prior to harvest did not reduce PFRF sufficiently. In contrast, no rate or timing of ethephon studied induced a reduction in ‘Chelan’ PFRF sufficient for mechanical harvest. Accompanying PFRF analyses, fruit quality was assessed by measuring firmness (g mm⁻¹), soluble solids (oBrix), weight (g) and color (CTIFL, scale 1–7). Ethephon applied 22 days before harvest at a rate of 3.5 L ha⁻¹ enhanced exocarp color in ‘Bing’ by 27%, while reducing firmness in both ‘Bing’ (−19%, 22 days prior to harvest) and ‘Chelan’ (−15%, 20 days prior to harvest). We observed a significant natural decline in ‘Skeena’ PFRF to levels acceptable for mechanical harvest. This research documents genotypic-specific pedicel-fruit abscission characteristics and the potential to facilitate mechanical harvest of fresh market quality sweet cherry fruit using ethephon.     

Pre-harvest foliar application of Prohexadione-Ca and gibberellins modify canopy source-sink relations and improve quality and shelf-life of ‘Bing’ sweet cherry

This research evaluated the potential of gibberellins (GA), and Prohexadione-Ca (PCa) to affect sweet cherry (Prunus avium) fruit size and quality. The results demonstrate the ability of ostensibly counter-acting plant growth regulators to significantly improve sweet cherry cv ‘Bing’ fruit size, fruit quality and postharvest characteristics compared to the current commercial application of GA₃ alone. In 2008, we found that the combination of GA₃ or GA_4/7 (30 mg l⁻¹) with PCa (150 mg l⁻¹) applied to entire 3-year-old limbs 30 days after anthesis increased fruit size and improved fruit quality in ‘Bing’. In 2009, we investigated the effect of application timing in larger-scale field trials, comparing treatments made at 30 or 37 days after anthesis, on fruit quality, storability and sensory attributes after storage. Treatment with PCa + GA₃ or PCa + GA_4/7 delayed fruit maturity by about 7 days compared to the untreated control. Both the first and second applications of PCa + GA_4/7 resulted in 35–40% fruit being ≥10 g, compared with only 20% in the control. PCa + GA₃ treatment also showed greater potential for improving fruit storability by maintaining fruit firmness, sweetness, and consumer appeal than PCa + GA_4/7. PCa alone or in combination with GAs inhibited current shoot growth and delayed fruit coloring development. After 30 days of 4°C storage, fewer than 5% fruit from untreated trees were rated as healthy and marketable, compared to 50 and 30% fruit from PCa + GA₃ treatment applied at 30 or 37 days after anthesis, respectively. In conclusion, preharvest foliar application of PCa + GA₃ at the onset of Stage II of fruit development shows potential to affect canopy source-sink relations and improved quality and shelf life of ‘Bing’ sweet cherries.     

Differential effects of abscisic acid and ethylene on the fruit maturation of <Emphasis Type="Italic">Litchi chinensis</Emphasis> Sonn.

Two litchi cultivars, a well-coloured ‘Nuomici’ and a poorly coloured ‘Feizixiao’, were used to investigate changes in endogenous abscisic acid (ABA) concentration and ethylene production during fruit maturation and to test the effects of exogenous growth regulators on litchi fruit maturation. Abscisic acid concentration in both the aril and pericarp increased with fruit maturation. Transfusion of ABA into the fruit 3 weeks before harvest accelerated, whereas transfusion of 6-benzyl aminopurine (6-BA) retarded sugar accumulation and pigmentation. The effect of 6-BA was assumed to link with the resultant decrease in ABA. In contrast, 1-aminocyclopropane-1-carboxylic acid (ACC) concentration and ACC oxidase (ACO) activities in the aril remained relatively constant during sugar accumulation. Transfusion of aminooxyacetic acid (AOA) significantly decreased ACC concentration but had no effect on sugar accumulation in the aril. These results suggested that endogenous ABA, but not ethylene, was critical for the sugar accumulation. However, the roles of ABA and ethylene in pericarp pigmentation were rather complicated. Application of exogenous ABA promoted anthocyanin synthesis significantly, but had very little effect on chlorophyll degradation. Ethylene production in litchi fruit decreased with development, but a transient increase of endogenous ethylene production was detected just around the colour break in ‘Nuomici’. Enhanced ACO activity in the pericarp was detected during pigmentation. Ethrel at 400 mg l⁻¹ showed no effect on pericarp coloration, but accelerated chlorophyll degradation and anthocyanin synthesis at a much higher concentration (800 mg l⁻¹). Fruit dipped in ABA solution alone yielded no effect on chlorophyll degradation, but the combined use of ABA and Ethrel at 400 mg l⁻¹ enhanced both chlorophyll degradation and anthocyanin synthesis. These results indicated the possible synergistic action of ethylene and ABA during litchi fruit colouration. ABA is suggested to play a more crucial role in anthocyanin synthesis, while ethylene is more important in chlorophyll degradation. ABA can increase the sensitivity of pericarp tissue to ethylene.     

Ethephon and Aventrol as tools to enhance spring rape productivity

Ethephon and Aventrol were used as tools to provoke the processes taking part in the formation of rape seed yield and quality. Investigations on spring rape (Brassica napus L.) cultivars ‘Terra’ and ‘Landmark’ were carried out from 2008–2010. Ethephon (10 mM) and Aventrol (1 l/ha — pinolene 960 g/l) were used on different plant growth stages: BBCH-62–64 and BBCH-72–74, BBCH-80–82, respectively. Impact of ethephon manifested itself as activation of ethylene evocation by siliqua and a slight activation of growth of siliqua dehiscence zone. Siliqua cell plasmalemma and tonoplast H⁺-ATPases activation under the influence of ethephon occurred but did not lead to the destruction of transmembrane electrochemical potential. Extra seed yield and crude fat yield increased; tendency towards a lowering of the saturated/unsaturated fatty acid ratio was observed. Under the influence of Aventrol the dehiscence zone of siliqua was more closed when compared to the control and the ethephon treated variants, seed loss was significantly lowered and transmembrane cation transport was not damaged. The seed yield increased, and this was due to the accumulation of extra crude fat. Aventrol did not change the fatty acid content in rape seed oil. The positive impacts of ethephon and Aventrol for spring rape seed yield formation and possible mechanisms are discussed.     

The influence of plant growth regulators and storage on root induction and growth in <Emphasis Type="Italic">Pelargonium zonale</Emphasis> cuttings

The effects of post harvest application of ethylene, abscisic acid (ABA), indole-3-butyric acid (IBA) treatments or dark storage on root induction and continued growth of regenerated roots in Pelargonium cuttings were investigated using hydroponics in the greenhouse. Ethylene markedly increased rooting percentage in ‘Greco’ and ‘Surfing’, reduced the number of roots per cutting in ‘Surfing’ and had no effect on the total root lengths in the two cultivars. Ethylene treatment reduced fresh root mass in ‘Surfing’, increased dry root mass and reduced root water content in both cultivars. ABA (50 μM) enhanced rooting percentage in ‘Greco’, reduced the number of roots per cutting, reduced total root lengths and fresh root mass in both cultivars. ABA increased dry root mass and reduced root water content in ‘Surfing’ but this effect was not apparent in ‘Greco’. Storing cuttings in the dark for 4 days had no effect on rooting percentage and number of roots per cutting in ‘Greco’ and ‘Surfing’. However, dark storage reduced total root lengths in ‘Surfing’ and reduced fresh root mass in ‘Greco’. Dark storage had no effect on dry root mass and water content in both cultivars. Applying 4 μl l⁻¹ IBA in the rooting solution induced maximum (100%) root induction in ‘Surfing’. However, IBA reduced the number of roots per cutting in ‘Greco’, reduced total root lengths and fresh root mass in the two cultivars. IBA treatment profoundly increased and reduced dry root mass and root water content, respectively, in ‘Greco’ and ‘Surfing’. The enhanced root induction observed after IBA and ABA applications could be ascribed to their influence on ethylene biosynthesis, since ethylene treatment increased rooting percentage in both cultivars. However, high ABA (100 μM) and IBA (12 μl l⁻¹) levels or dark storage reduced the ability of induced roots to continue growth. We attribute our results to plant stress-response mechanism and ethylene appears to play an important role in the process of root initiation and root growth in Pelargonium cuttings.     

Assaying for Pollen Drift from Transgenic ‘Rainbow’ to Nontransgenic ‘Kapoho’ Papaya under Commercial and Experimental Field Conditions in Hawaii

In 1992, papaya ringspot virus (PRSV) was discovered in the Puna district of Hawaii island where 95% of the state of Hawaii’s papaya was being grown. By 1998 production in Puna had decreased 50% from 1992 levels. A PRSV-resistant transgenic papaya ‘Rainbow’ containing the coat protein gene of PRSV was released commercially in Hawaii in 1998, and saved the papaya industry from further devastation. In the ensuing years since the release of the transgenic papaya, a number of farmers grew hermaphrodite nontransgenic ‘Kapoho’ papaya in close proximity to plantings of hermaphrodite transgenic ‘Rainbow’ papaya. These plantings provided a unique opportunity to assay for transgenic-pollen drift under commercial conditions. Between 2004 and 2010, assays for the GUS (beta-glucuronidase) transgene in embryos were done to study transgenic-pollen drift in commercial ‘Kapoho’ plantings and in replicated field plots. Very low pollen drift (0.8%) was detected in fruit of ‘Kapoho’ trees in the border row of one plantation when 90 embryos were assayed per fruit, while no pollen drift was detected in four other commercial plantings in which eight embryos were tested per fruit. Pollen drift averaged 1.3% of tested embryos in field plots where individual hermaphrodite ‘Kapoho’ trees were adjacent to two or four ‘Rainbow’ trees. In contrast, 67.4% of tested embryos were GUS positive in similarly located female ‘Kapoho’ trees. The very low transgene flow to close-by ‘Kapoho’ plantings is likely due to the fact that hermaphrodite trees are used commercially in Hawaii and that these trees are largely self-pollinated before the stigma is exposed to external pollen.     

Evolution of early determinate tomato cultivars during the last three decades as a result of research conducted at Warsaw Agricultural University

Earliness is a crucial factor of tomato field production in Poland. A. Michalska and B. Kubicki (1978) conducted the first investigations on tomato earliness at the Department of Plant Genetics and Breeding. The main conclusions from these studies indicated that it was possible to obtain varieties earlier than ‘New Yorker’ as a result of transgression. The two new varieties (‘Alfa’ and ‘Akord F₁’) proved to be two weeks earlier than ‘New Yorker’. However, earliness was correlated with smaller fruit weight (30–40 g). At the next stage of experiment some improvement was achieved both in the size of fruit (45 g for ‘Beta’ up to 70 g for ‘Alka’) as well as colour intensity and good flavour. With the next few years fruit weight was still increased (up to 100 g for ‘Maskarena’) and a higher level of firmness was obtained (mid firm fruits for ‘Maskarena’ and ‘Delta’). At present, the Polish Research Centre for Cultivar Testing recommends our varieties ‘Betalux’, ‘Promyk’ and ‘Delta’ as standards.     

Plantlet regeneration of <Emphasis Type="Italic">Kappaphycus alvarezii</Emphasis> var. adik-adik by tissue culture

Three color morphotypes of Kappaphycus alvarezii var. adik-adik (brown, green and red) collected from a farming area in Tictauan Is., Zamboanga City, Philippines were used as explants in the study in order to micropropagate ‘new’ plants. Individual sections of sterile Kappaphycus alvarezii var. adik-adik, initially cultured in a 48-well culture plate containing ESS/2 + E3 + PGR, released callus cells after 4–5 days of incubation at 23–25°C, 13:11H LD cycle and 10–15 μmol photons m⁻² s⁻¹ light intensity. True calli were formed after 29–35 days following dense formation of filaments or undifferentiated round cells at the medullary and inner cortical layers of the section. Plantlets (2–3 mm long) of Kappaphycus alvarezii var. adik-adik were able to regenerate after 98, 150 and 177 days in-vitro among the reds, greens, and browns, respectively. This study established successful methods for the production and regeneration of tissue explants of Kappaphycus alvarezii var. adik-adik which can possibly be used to mass produce ‘new’ cultivars for land- and sea-based nurseries as sources for commercial farming. Presented at the 6th Meeting of the Asian Pacific Society of Applied Phycology, Manila, Philippines.     

Identification and stability of QTLs for fruit quality traits in apple

Breeding for fruit quality traits is complex due to the polygenic (quantitative) nature of the genetic control of these traits. Therefore, to improve the speed and efficiency of genotype selection, attention in recent years has focused on the identification of quantitative trait loci (QTLs) and molecular markers associated with these QTLs. However, despite the huge potential of molecular markers in breeding programmes, their implementation in practice has been limited by the lack of information on the stability of QTLs across different environments and within different genetic backgrounds. Here, we present the results from a comprehensive analysis of the inheritance of fruit quality traits within a population derived from a cross between the apple cultivars ‘Telamon’ and ‘Braeburn’ over two successive seasons. A total of 74 different QTLs were identified for all the major fruit physiological traits including fruit height, diameter, weight and stiffness, flesh firmness, rate of flesh browning, acidity, the oBrix content and harvest date. Seventeen of these QTLs were ‘major’ QTLs, accounting for over 20% of the observed population variance of the trait. However, only one third (26) of the identified QTLs were stable over both harvest years, and of these year-stable QTLs only one was a major QTL. A direct comparison with published QTL results obtained using other populations (King et al., Theor Appl Genet 102:1227–1235, 2001; Liebhard et al., Plant Mol Biol 52:511–526, 2003) is difficult because the linkage maps do not share a sufficient number of common markers and due to differences in the trait evaluation protocols. Nonetheless, our results suggest that for the six fruit quality traits which were measured in all populations, nine out of a total of 45 QTLs were common or stable across all population × environments combinations. These results are discussed in the framework of the development and application of molecular markers for fruit quality trait improvement.     

The development of techniques for tissue culture of mango (<Emphasis Type="Italic">Mangifera indica</Emphasis> L.) var. Carabao and successful transfer of <Emphasis Type="Italic">ex vitro</Emphasis>-grafted plants to soil and the field

The mango, a virtually neglected fruit before the advent of nitrate-induced flowering, is now the third leading export fruit in the Philippines, with the ‘Carabao’ mango being the only variety exported. Delay or control of ripening, as well as the ability to program market availability, would further increase the value of mango. Prolonging its shelf life and improving other characteristics can be achieved through biotechnology, requiring a reliable tissue culture regeneration protocol, and a successful transfer-to-soil system. Between 2004 and 2008, immature fruits were collected and cultured in vitro. Primary somatic embryo (SE) induction ranged from 16–100% depending on the strain, collection time, and tree source. A single SE was required to initiate SE proliferation. When subcultured, the SEs proliferated, germinated, and produced plantlets. Initial shoot formation was 8–64%, while succeeding true leaf formation was reduced to 0–36%. In some cultures, abscission and browning were observed, but gas chromatography assays ruled out ethylene as the cause. Regenerated plants survived transfer to soil, but at low percentages. While it took 1 y to develop the tissue culture protocol, it took 3 y to develop the technique for successful transfer of plantlets to soil, and to the field. This is the first report, of a polyembryonic mango, variety Carabao, for which successful tissue culture and field transplantation systems were developed. The technology is equally important as a way to rapidly propagate uniform rootstocks of superior ‘Carabao’ strains or other varieties, for generation of variability, genetic transformation, and for germplasm conservation and exchange.     

Forced flowering of pineapple (<Emphasis Type="Italic">Ananas comosus</Emphasis> cv. Tainon 17) in response to cold stress,ethephon and calcium carbide with or without activated charcoal

Ethylene, a gaseous plant hormone, is responsible for the initiation of reproductive development in pineapple. Reproductive development can be forced in pineapple (Ananas comosus var. comosus) throughout the year with ethylene. Inhibition of natural flowering initiation with aviglycine [(S)-trans-2-amino-4-(2-aminoethoxy)-3-butenoic acid hydrochloride], an inhibitor of ethylene biosynthesis, provides evidence that reproductive development in response to cold stress and short daylength is also in response to ethylene production. We studied the effect of cold treatment of pineapple on ethylene production and flower induction by applying a short-term cold stress to stem apices. Shoot apices of pineapple treated with ice crystals also produced twice as much ethylene as did those of control plants and significantly more than was produced by “D” leaf basal tissue. Moreover, pineapple plants treated four times with ice crystals or ice water were induced to flower under field conditions and the forcing efficiency, as evaluated by the percentages of inflorescence emergence and fruit harvest, was comparable to forcing with calcium carbide (CaC₂) and ethephon. In another field experiment two applications of a 1.0% solution of CaC₂ or 0.15% ethephon applied at 48 h intervals was sufficient to force reproductive development of ‘Tainon 17’. Furthermore, 0.5 or 1.0% solutions of CaC₂ supplemented with 0.5% activated charcoal (AC) significantly improved the forcing effectiveness of CaC₂. This could/would make it possible to reduce the number or concentration, or both, of CaC₂ required to effect forcing in pineapple.     

Variation in performance on two grape cultivars within and among populations of grape Phylloxera from wild and cultivated habitats

When an indigenous insect becomes a pest, comparisons of performance of pest and non-pest populations on crop plants and of genetic variation in that performance may provide insight into the evolution of pest populations. To measure such genetic variation, 8–15 clones of the grape phylloxera (Daktulosphaira vitifoliae Fitch) were collected from wild grapevines in each of 3 geographically isolated sites (populations) and from commercial vineyards in northern California. A complete life table was made for clonal replicates from populations collected from wild grapevines on each of two commercial grape cultivars, the susceptibleVitis vinifera (L.) cultivar Cabernet Sauvignon, and the phylloxera-resistant rootstock ‘AxR # 1’. Variation in mean performance on these two hosts was partitioned among clones within collection sites and among sites. Performance measures included an individual analog to the intrinsic rate of increase (r), age at first oviposition, fecundity in the first ten days of reproduction, total fecundity, and longevity. The overall performance of phylloxera from the wild grapevines on the resistant cultivar AxR # 1 was greater than or equal to that on the susceptible cultivar Cabernet Sauvignon. There was significant variation among clones within populations from wild grapes in the rate of increase on ‘AxR # 1’ and marginally significant clonal variation in some of the component paramters. There was no significant variation among clones within populations on ‘Cabernet Sauvignon’ and no significant differences between populations on either crop in any trait. In a second experiment we compared the relative performance of 15–17 clones from wild grapevines and from commercial vineyards when reared on ‘Cabernet Sauvignon’ and ‘AxR # 1’. Phylloxera from commercial vineyards had much higher overall performance on ‘Cabernet Sauvignon’ than did phylloxera from the wild grapevines. Phylloxera from the commercial vineyard also had higher performance on ‘Cabernet Sauvignon’ than on ‘AxR′ 1’ but the performance of the phylloxera from wild and commercial grapes did not differ on ‘AxR # 1’. Our results show that there is genetic variation in traits related to performance on a resistant rootstock within these indigenous non-pest populations of phylloxera, but not among them. The pattern of performance of pest and non-pest populations on two commercial cultivars suggests that current levels of phylloxera performance on crop cultivars are the result of adaptation to those cultivars which has occurred while phylloxera has been associated with viticulture. Implications of these results for understanding the recent adaptation of phylloxera to ‘AxR # 1’ in California are also discussed.     

Ethylene action blockade and cold storage affect ripening of ‘Golden’ papaya fruit

The purpose of this work was to evaluate the effects of ethylene action blockade and cold storage on the ripening of ‘Golden’ papaya fruit. Papayas harvested at maturity stage 1 (up to 15% yellow skin) were evaluated. Half of the fruits, whether treated or not treated with 100 nL L⁻¹ of 1-methylcyclopropene (1-MCP), were stored at 23°C, while the other half were stored at 11°C for 20 days prior to being stored at 23°C. Non-refrigerated fruits receiving 1-MCP application presented a reduction in respiratory activity, ethylene production, skin color development and pectinmethylesterase activity. Even with a gradual increase in ethylene production at 23°C, fruits treated with 1-MCP maintained a high firmness, but presented a loss of green skin color. Cold storage caused a decrease in ethylene production when fruits were transferred to 23°C. The results suggest that pulp softening is more dependent on ethylene than skin color development, and that some processes responsible for loss of firmness do not depend on ethylene.     

Exogenous gibberellic acid increases the fruit weight of ‘Comte de Paris’ pineapple by enlarging flesh cells without negative effects on fruit quality

In mainland China, the most popular pineapple cultivar is ‘Comte de Paris’. Gibberellic acids have been widely applied to enhance fruit growth in various species. To evaluate the effect of gibberellic acid (GA₃) on ‘Comte de Paris’ pineapple production and quality, pineapple fruits were sprayed with GA₃ at concentrations of 5, 20, 50, or 100 mg l⁻¹ at both 0 and 15 days after flowering (DAF). Fruits were sampled every 15 days from 0 to 60 DAF (maturation) for flow cytometric analysis and histological observation. The results showed that the treatments with the three highest concentrations of GA₃ significantly increased fruit weight, and the most effective concentration was 50 mg l⁻¹ GA₃, which increased the flesh weight by 20.3% compared to the control. Although treatment with GA₃ had little effect on the total soluble solids and fruit juice pH, it increased the vitamin C content. Although flow cytometric analysis showed that the 50 mg l⁻¹ GA₃ treatment had only a slight impact on the number of S phase cells, histological observations indicated that the increase of fruit volume and flesh weight under this GA₃ treatment was not due to the increase of cell number but a result of the increase of cell area in the fruit flesh.     

Selection of Highly Informative Microsatellite Markers to Identify Pollen Donors in ‘Hass’ Avocado Orchards

‘Hass’ is the most popular avocado (Persea americana Mill.) cultivar in the world. It has been characterized as a crop requiring cross-pollination. However, the potential extent of self-pollination and the most effective pollen donors (best cross-pollinizing cultivars) have not been determined. In this study, 56 markers were screened against ‘Hass’ and nine commonly used pollinizing cultivars grown in southern California: ‘Bacon,’ ‘Ettinger,’ ‘Fuerte,’ ‘Harvest,’ ‘Lamb Hass,’ ‘Marvel,’ ‘Nobel,’ ‘Sir Prize,’ and ‘Zutano.’ Seventeen microsatellite, i.e., simple sequence repeat (SSR) markers, were found to be very promising for paternity analysis. Four highly informative SSR markers were selected to accurately and unequivocally identify pollen parents of ‘Hass’ fruit from an orchard interplanted with these pollinizing cultivars. From 2003 to 2006, 7,984 ‘Hass’ fruit were analyzed for their paternity. Overall, the pollen parents of 99.55% of the analyzed fruit could be unequivocally identified with a single multiplex polymerase chain reaction (PCR). Only 36 fruits (<0.45%) required a second PCR reaction to reach unequivocal identification of the pollen parents.