Stone Fruit Industry Research Articles

THE EFFECT OF TWO NEMATODE SPECIES (MELOIDOGYNE JAVANICA AND CRICONEMOIDES XENOPLAX) ON SOUTH AFRICAN-BRED STONE FRUIT ROOTSTOCKS SCREENED UNDER CONTROLLED CONDITIONS

The future banning of soil fumigants by 2015 is likely to have a negative impact on the South African stone fruit industry. The industry is currently dependent on a few high-chill imported commercial rootstocks that, in many cases, are not adapted to local soil and climatic conditions. Plant-parasitic nematodes are a severe problem worldwide, with serious economic implications for the fruit industry. Therefore, the continuous improvement and the development of crops with increased resistance or tolerance to pests and diseases, as well as to harsh environmental conditions is of importance. In South Africa the most important plant-parasitic nematodes on stone fruit rootstocks are Criconemoides xenoplax (ring nematode) and Meloidogyne javanica (root-knot nematode). Agricultural Research Council (ARC)-bred stone fruit hybrids were screened for nematode resistance or tolerance under controlled conditions during 2009/10 and 2010/11 at the ARC Infruitec-Nietvoorbij facility at Bien Donne Experimental Farm, Simondium, Western Cape. Screening was done on rooted cuttings in black nursery bags, in a complete randomised block design housed in a greenhouse to evaluate the effect of the two nematode species. Inoculum of C. xenoplax was produced using the peach cultivar ‘Atlas’ as host and for M. javanica the tomato cultivar ‘Moneymaker’. A concentration of 2,000 J2 C. xenoplax in 100 ml soil, and 2,000 eggs M. javanica in water, was added to each plant. After a period of six months, C. xenoplax were extracted from the soil, using a sugar flotation technique and the number of nematodes per 250 g of soil determined. For M. javanica, the soil was washed from the roots and the roots were scored according to a gall index on a scale from 0 to 5. To date, the stone fruit rootstock breeding programme has bred very promising stone fruit rootstocks that are suitable for South African commercial growers and emerging farmers.

A somaclonal myrobalan rootstock increases waterlogging tolerance to peach cultivar in controlled conditions

Plants are aerobic organisms that require the availability of O2 for nutrient uptake, so excess water surrounding roots can generate lethal conditions. Therefore a new flood-tolerant stone-fruit rootstock was used in a grafted combination with peach cv Suncrest (Prunus persica (L.) Batsch.) used as scion, to test its tolerance strength during a twenty-one day flooding period. Potted plants, from graft combination of cv Suncrest with rootstock Mr.S 2/5 wild type (Prunus cerasifera Erhr) and its clone variant (S.4), were submitted to normoxic and flooded stress for 21 days, under open conditions. Suncrest/S.4 plants had the highest plant growth under normoxic condition and the highest plant survival under flooded conditions. Under flooded conditions a halt in plant growth and the appearance of severe damage were detected in the Suncrest/wt plants. In the latter, symptoms of flooding were desiccation of the shoot apex, strong reddening of leaves followed by appearance of necrotic areas and senescence of almost all leaves.The responses observed in all organs of the grafted plant could be linked to relevant morpho-physiological adaptations to flooding that would ensure survival during short periods of anoxia. Results also provided evidence that flooding tolerance was conferred by the S.4 clone to the scion. The availability of a novel rootstock tolerant to short-term waterlogging conditions will offer new possibilities to the stone-fruit industry located in various adverse environments.

FORCED-AIR COOLING REDUCES 1-MCP APPLICATION DURATION ON PLUMS (PRUNUS SALICINA LINDL.) WITHOUT REDUCING EFFECTIVENESS

FORCED-AIR COOLING REDUCES 1-MCP APPLICATION DURATION ON PLUMS (PRUNUS SALICINA LINDL.) WITHOUT REDUCING EFFECTIVENESS

"HoneySweet" Plum—A Valuable Genetically Engineered Fruit-Tree Cultivar

“HoneySweet” is a plum variety developed through genetic engineering to be highly resistant to plum pox potyvirus (PPV) the causal agent of sharka disease that threatens stone-fruit industries world-wide, and most specifically in Europe. Field testing for over 15 years in Europe has demonstrated the stable and durable PPV resistance of “HoneySweet”. Resistance is based on gene silencing whereby the inserted gene induces a natural plant defense mechanism against viruses. This resistance has been transferred to seedlings through cross-hybridization as a single locus dominant trait making it useful as a parent for developing new plum varieties for specific growing areas and markets. “HoneySweet” plums are of high quality and compare well to the quality and nutritional value of conventional plums. “HoneySweet” demonstrates the utilization of genetic engineering to provide safe and effective solutions to important agricultural challenges facing growers, and ultimately consumers.

First Report of Cylindrocarpon pauciseptatum Associated with Root Rot and Decline of Peach in Southern Italy (Apulia Region).

During a survey for the sanitary status of stone fruits in southern Italy (Apulia region), symptoms of low vigor, sparse foliage, and chlorosis of leaves, frequently leading to decline or death of the plants, were observed on 3- to 5-year-old peach trees (Prunus persica) cvs. Tardi Belle, Zee Lady, and O'Henry grafted on GF677. Brown-to-black discolorations of the wood were observed in cross-sections of the trunks just below the graft union. Samples were collected from May to June 2010 from two symptomatic orchards in Brindisi and Foggia provinces. Small pieces of brownish, vascular wood and necrotic root tissues were surface disinfested, placed onto potato dextrose agar (PDA), and incubated for 7 days at 25°C in the dark. Single-conidial isolates were subsequently grown on PDA at 25°C for 10 days. Fungal colonies were presumptively identified as members of the genus Cylindrocarpon on the basis of their morphological and conidial characteristics. On PDA, the isolates developed abundant mycelium, which gradually became yellowish or partially brownish. Macroconidia were predominantly three septate, straight and cylindrical with both ends broadly rounded. Chlamydospores and ovoidal microconidia were observed on synthetic nutrient-poor agar (1). Sequence of the ribosomal internal transcribed spacer (ITS) region was obtained using universal primers (ITS6-ITS4) and deposited in GenBank (Accession No. HE577846). This sequence revealed 100% genetic identity with a sequence from Cylindrocarpon pauciseptatum Schroers & Crous (Accession No. EF607090), a recently described species (3). In nature, several species of the genus Cylindrocarpon affect a large number of woody plants, mainly grapevine, olive, and stone fruits, in which they attack the root surface (2). To verify Koch's postulates, the roots of 20 3-month-old peach seedlings (GF305) were dipped for 30 min in a spore suspension of the fungus (1 × 108 conidia ml-1). Seedlings were then transplanted in an artificial soil mix and held under controlled conditions in a greenhouse at 24°C. Typical black-foot symptoms developed on 92% of the inoculated plants within 3 months, whereas the control plants, whose roots had been dipped in distilled water, remained healthy. C. pauciseptatum was reisolated from infected tissues and internal vascular lesions of 45% of the inoculated plants, but none of the plants used as controls, fulfilling Koch's postulates. To our knowledge, this is the first report of this pathogen on peach in the Apulia Region of Italy. Currently, C. pauciseptatum is limited to a few orchards where presumably it was introduced with infected propagating material from extra-regional nurseries. C. pauciseptatum has the potential to negatively affect the stone fruit industry in Italy including reducing nursery production and productivity and vigor of trees in orchards, or even rapid death of young trees.

Harvest maturity indicators in the stone fruit industry

Harvest maturity indicators in the stone fruit industry

Comparison of RT-PCR and PCR-RFLP molecular techniques used for the differentiation of isolates belonging to D and M strains of Plum pox virus collected from Cluj region.

Plum pox virus (PPV) is the causal agent of sharka disease, which is responsible for severe damage and important economic losses in the stone fruit industry. The disease mainly affects stone-fruit species, mainly apricot, plum and peach . Sharka is originated from Eastern Europe and was described for the first time around 1915 in Bulgari a (Atanasoff, 1932). In this study we collected thi rty PPV isolates from one experimental orchard belonging to the Fruit Research and Development Station Cluj. Molecular strain differentiation was done with the help of RT-PCR technique by analyzing the genomic region (Cter)CP of the virus by using RFLP analysis we were able to distinguish the two major strains, D and M, based on Rsa I polymorphism located in the genomic region (Cter) CP.

Susceptibility of Prunus rootstocks to natural infection of Plum pox virus and effect of mineral oil treatments

The use of rootstocks that are less susceptible or resistant to natural Plum pox virus (PPV) infection and/or the application of mineral oil treatments are two possible strategies to reduce viral incidence in nursery plots. We evaluated the susceptibility of Prunus rootstocks used in the Spanish stone fruit industry and the effect of mineral oil treatment (Sunspray Ultrafine at 1%) on the spread of the virus at two different localities in Valencia, Spain, under different natural PPV inoculum pressures (high inoculum pressure, 2006‐08; low inoculum pressure, 2006‐07). Samples from both plots were analysed by double-antibody sandwich indirect enzyme-linked immunosorbent assay (DASI-ELISA) and spot real-time RT-PCR. Under high inoculum pressure, the assayed rootstocks exhibited significant differences in their susceptibility to natural infection. The most susceptible rootstocks at the end of the experiment were Adesoto 101 and Mariana GF8-1. Cadaman and Garnem rootstocks presented the fewest PPV-infected plants; these infections could be detected only by spot real-time RT-PCR. No differences among the assayed rootstocks were found under low PPV inoculum pressure. Aphid species were monitored using Moericke yellow water traps and sticky-plant methods at both localities in May 2006 and 2007. Aphis spiraecola was the most abundant aphid species monitored by both methods at both localities. The average percentage of A. spiraecola carrying PPV PCR-amplifiable targets was 30.37% in the plot with high PPV inoculum pressure and only 7.98% in the plot with low inoculum pressure. We found significant differences in PPV incidence between Mariana GF8-1 plots that were treated with mineral oil and those that were not treated after one year under natural conditions and high PPV inoculum pressure.

Control and monitoring: phytosanitary situation of Plum pox virus in Australia

Sharka disease does not occur in Australia and is recognized as the most serious disease threat to Australia's stone fruit industry. Strategies are in place to minimize the risk that exotic diseases like sharka should establish in Australia. These are achieved by implementing: (1) pre‐import measures to reduce the threat of entry; (2) controls at the point of entry and (3) response and contingency planning to contain or eradicate any incursions into Australia. An active and on‐going awareness programme within the Australian stone fruit industry is aimed at early detection of sharka disease in the orchard.

Adoption of sustainable irrigation management practices by stone and pome fruit growers in the Goulburn/Murray Valleys, Australia

The management of water resources by orchards in the south-eastern region of Australia is an increasingly important policy issue, especially given the low water allocations and concerns about salinity in recent years. Optimal management for economic and environmental sustainability can be described as best management practice (BMP). A project was developed to run an extension program, which aimed to achieve behavioural change among orchardists through the adoption of irrigation BMPs and benchmarks. The effectiveness of the extension program was evaluated and the drivers for adoption assessed. In the first stage of the project both BMPs and benchmarks were determined for irrigation management. A survey of 200 growers showed no relationship between yield and irrigation system or irrigation volume suggesting that increased yields were not a key driver for adoption of sustainable irrigation practices. Stage two of the project involved undertaking an extension program aimed to facilitate the adoption of BMPs and benchmarks and incorporated a suite of activities to meet the learning needs of a diversity of participants (40 growers). The program was effective in establishing behavioural change for many of the growers involved; however, it was resource intensive requiring significant one-on-one input. Stage three aimed to analyse the key drivers for adoption of sustainable irrigation practices for the whole of the stone and pome fruit industry in south-eastern Australia using market research. The study determined that water use efficiency was not a key driver for adoption of sustainable irrigation practices (micro irrigation and soil moisture monitoring) and adoption was generally not limited by lack of knowledge. Groups of growers were identified where extension programs could be effective by focussing on specific information e.g. redevelopment of orchard. Other groups had no need and/or ability to change unless the external operating environment was to change e.g. regulation, access to pressurised water. The voluntary adoption of more sustainable irrigation practices will probably require extensive resources using one-on-one methodology. The extension program should not focus on the broader social objective of improved water use efficiency but promote other potential benefits (e.g. labour saving, redevelopment of production systems, management flexibility) with targeted messages for specific groups.

Stylet Penetration by Adult <I>Homalodisca coagulata</I> on Grape: Electrical Penetration Graph Waveform Characterization, Tissue Correlation, and Possible Implications for Transmission of <I>Xylella fastidiosa</I>

The sharpshooter Homalodisca coagulata (Say) (Hemiptera: Cicadellidae: Cicadellinae) is an exotic vector of the Pierce’s disease (PD) bacterium, Xylella fastidiosa (Wells et al.), that was first observed in California in 1989. H. coagulata has since greatly increased the threat of PD to the grape industry as well as stone fruit, nursery, and ornamental industries in California. This is the first in a series of articles that together describe how sharpshooter stylet penetration behaviors (especially intricate stylet activities, salivation, and ingestion) control transmission (i.e., acquisition and inoculation) of X. fastidiosa. Herein, we categorized and characterized alternating current electrical penetration graph (EPG) waveforms from glass-winged sharpshooter stylet penetration on petiole of susceptible grape (‘Cabernet Sauvignon’), paying special attention to waveform fine structures that are likely to be the key to detecting the instant of inoculation. We also correlated waveforms with salivary sheath termini in grape tissues. For the first time in any EPG study of leafhopper or planthopper feeding, we demonstrate through case studies of individual probes how to follow the process of stylet penetration step by step as it is occurring, including salivary sheath branching and when the stylets first puncture a xylem cell. Finally, we discuss the implications of our findings for understanding the transmission mechanism of X. fastidiosa, in comparison with hypothesized mechanisms in the literature.

NONDESTRUCTIVE ASSESSMENT OF PEACH AND NECTARINE FIRMNESS

Controlled ripening or conditioning of peaches and nectarines is an increasingly important component of the Australian stonefruit industry. This process involves monitoring fruit firmness during a postharvest conditioning period at 20 °C. This destructive monitoring currently uses a penetrometer (7.9 mm tip) and must be done at regular intervals during the ripening process. This is not only time consuming but also costly. Two commercial nondestructive measures of fruit firmness (Acoustic firmness sensor and the Sinclair iQ system) were assessed as an alternative to the manual penetrometer for the determination of fruit firmness in two peach and two nectarine cultivars. The results revealed large variations in firmness among the fruit of each cultivar as measured by all instruments. We modeled fruit softening data from the Sinclair iQ system and destructive penetrometer to predict when the fruit were ready for retail distribution. This model needs to be further evaluated and refined, but its commercial application would be a significant benefit for the peach and nectarine fruit conditioning programs. This would save labour costs and reduce the amount of fruit required for destructive testing.

Using market research to understand the adoption of irrigation management strategies in the stone and pome fruit industry

Market research was conducted to develop an extension program targeting the specific irrigation management needs of growers in the stone and pome fruit industry within the Goulburn Valley, Victoria. The process of integrating market research with extension practice proved challenging, as it required the development of an extension program that was fundamentally different from what was originally envisaged. However, it was essential to achieve this integration in order to meet the original objectives for the extension program as set by the funding body. We found, in most cases, that the motivation for stone and pome fruit growers in the Goulburn Valley to change orchard irrigation management practices was not because they needed to save water, or to increase water use efficiency. Instead, growers were changing practices in order to save time irrigating, improve the scope for managerial flexibility in the orchard, or when redeveloping their orchard to a closer planting design. These findings suggest that growers in the Goulburn Valley are more likely to respond to an extension program consistent with these motivations rather than a program promoting water use efficiency.

CHEMICAL REST BREAKING AGENTS FOR THE SOUTH AFRICAN POME AND STONE FRUIT INDUSTRY

ISHS XXVI International Horticultural Congress: Key Processes in the Growth and Cropping of Deciduous Fruit and Nut Trees CHEMICAL REST BREAKING AGENTS FOR THE SOUTH AFRICAN POME AND STONE FRUIT INDUSTRY

ROOTSTOCK BREEDING FOR STONE FRUITS

Over the last 20 years stone fruit rootstock development has begun shifting from seedling to clonal types, many of interspecific origin. Publicly funded breeding programs have produced most of these rootstocks due to the time, cost, and risk associated with their development; however, private industry is emerging as a significant contributor of many of the newer rootstocks. Particularly noteworthy among recent releases has been the incorporation of resistance to soilborne diseases, nematodes, waterlogging and vigor control, the last most notably in recent cherry rootstocks. Nevertheless, despite the remarkable progress in the development of clonal stocks, seedling rootstocks still dominate most stone fruit industries around the world, if only because of their relatively low cost, ease of propagation, and proven utility. Many opportunities and challenges remain to be addressed in the areas of disease and insect resistance, adaptation to biotic and abiotic stresses, graft compatibility, and rootstock influence on scion performance and fruit quality. Biotechnology is beginning to show potential in accelerating rootstock development. With the development of markers to assist selection for difficult to evaluate traits, new rootstocks with resistance to multiple diseases are feasible. Future prospects for breeding are presented. INTRODUCTION Several surveys have been undertaken to determine the relative importance of the various “problems” facing stone fruit industries around the world. The peach (Prunus persica) industry has received the most attention, if only because of its large size, hence economic importance, relative to other stone fruit crop industries. Results of two of these surveys are summarized in Table 1. Relative order of importance changed little between 1982 and 1997. At this time it would appear that the need for waterlogging tolerance has been alleviated somewhat by recent releases. This factor was the only one that moved down significantly in importance since the earlier survey. Given the number of rootstock releases that offer some relative promise for most of the problem areas listed, this might seem surprising at first. However, given that orchard life expectations for stone fruits range from 15 to 25 years or longer, adoption is an inherently slow process. This may also be due in part to the fact that many interspecific rootstocks change other “non-target” characteristics of the finished tree, for example, vigor or bloom date which require changes in management that growers may not wish to change. Additionally, many “problem” sites have more than one limitation and require that a new rootstock incorporate resistance to multiple problems for successful adaptation. In many cases, new rootstocks are probably best suited for regional or prescription/niche planting rather than broad use over a large industry. Regional testing is the only way to determine each rootstock’s best adaptation. Priorities vary from one stone fruit crop to another. Rom (1991) has summarized priorities for apricots (P. armeniaca) which generally agreed with those cited for peach. Nematodes were of less importance and one particularly vexing issue with apricot was that of scion/rootstock graft compatibility. However, Rom noted that priorities also varied Proc. XXVI IHC – Genetics and Breeding of Tree Fruits and Nuts

PERCEPTIONS OF SUPPLY CHAIN MANAGEMENT FOR PERISHABLE HORTICULTURAL CROPS: AN INTRODUCTION

PERCEPTIONS OF SUPPLY CHAIN MANAGEMENT FOR PERISHABLE HORTICULTURAL CROPS: AN INTRODUCTION