Mixed Orchard Research Articles

Challenges of soil carbon sequestration in the NENA region

Abstract. The Near East North Africa (NENA) region spans over 14 % of the total surface of the Earth and hosts 10 % of its population. Soils of the NENA region are mostly highly vulnerable to degradation, and future food security will much depend on sustainable agricultural measures. Weather variability, drought and depleting vegetation are dominant causes of the decline in soil organic carbon (SOC). In this work the status of SOC was studied, using a land capability model and soil mapping. The land capability model showed that most NENA countries and territories (17 out of 20) suffer from low productive lands (> 80 %). Stocks of SOC were mapped (1:5 000 000) in topsoils (0–0.30 m) and subsoils (0.30–1 m). The maps showed that 69 % of soil resources are shown to have a stock of SOC below the threshold of 30 tons ha−1. The stocks varied between ≈10 tons ha−1 in shrublands and 60 tons ha−1 for evergreen forests. Highest stocks were found in forests, irrigated crops, mixed orchards and saline flooded vegetation. The stocks of soil inorganic carbon (SIC) were higher than those of SOC. In subsoils, the SIC ranged between 25 and 450 tons ha−1, against 20 to 45 tons ha−1 for SOC. Results highlight the contribution of the NENA region to global SOC stock in the topsoil (4.1 %). The paper also discusses agricultural practices that are favorable to carbon sequestration such as organic amendment, no till or minimum tillage, crop rotation and mulching and the constraints caused by geomorphological and climatic conditions. The effects of crop rotations on SOC are related to the amounts of above and belowground biomass produced and retained in the system. Some knowledge gaps exist, especially in aspects related to the impact of climate change and effect of irrigation on SOC, and on SIC at the level of the soil profile and soil landscape. Still, major constraints facing soil carbon sequestration are policy-relevant and socioeconomic in nature, rather than scientific.

Effect of mixed orchards on Population dynamics and dominant on Tephritid flies in the New Valley Governorate, Egypt

Effect of mixed orchards on Population dynamics and dominant on Tephritid flies in the New Valley Governorate, Egypt

Do floral resources influence pollination rates and subsequent fruit set in pear ( Pyrus communis L.) and apple ( Malus x domestica Borkh) cultivars?

Abstract Pear and apple are among the main fruit crops worldwide. These species can be planted in mixed orchards, and they both depend on insect pollination for fruit set. As pollinating insects are attracted by the floral resources, we investigated nectar and pollen production and chemical composition in four pear (‘Concorde’, ‘Conference’, ‘Doyenne du Comice’, ‘Triomphe de Vienne’) and five apple (‘Braeburn’, ‘Golden Reinders’, ‘Jonagored’, ‘Pinova’, ‘Wellant’) cultivars commonly grown in Belgium. We also investigated whether insect flower visitation rate and pollination efficiency are linked to floral resource quantity and quality. The pear cultivars flowered one week before the apple cultivars in early spring, and their flowers were about six times less visited by insects. The visitors foraged more on the pollen of the pear trees and the nectar of the apple trees. Pear flowers produced higher volumes of nectar than apple flowers (1.3–3.2 μl vs. 0.4-0.6 μl), but with lower sugar concentration (9.6%-10.8% vs. 28.3%-36.4%). Pear flowers also produced fewer pollen grains per anther than apple flowers (2425–4937 vs. 3284–7919), but these had higher polypeptide (346–362 μg/mg vs. 216–303 μg/mg), amino-acid (40–77 μg/mg vs. 12–18 μg/mg) and phytosterol (21–47 μg/mg vs. 15–43 μg/mg) concentrations. The foraging behavior of the insects is thus better explained by nectar and pollen quality rather than quantity. Despite the differences in flower visitation rates, pollination of both species resulted in valuable fruit production.

Management of carob tree orchards in Mediterranean ecosystems: strategies for a carbon economy implementation

This paper offers a different framework for managing Mediterranean drought carob-tree orchard ecosystems. Two dry-farming systems were compared during two consecutive years: pure productive orchards and mixed orchards in a total of 360 mature trees distributed by 18 plots with areas of 0.55 and 0.30 ha per plot, respectively. Carob, fig, almond and olive trees compose mixed orchards. Trees of the mixed orchards were more productive than those of pure orchards. The main problem of both systems was the large variability and the low fruit production due to non-bearing trees, inducing unfavorable economic returns. Yield varied between 7.7 and 28.5 kg tree−1 respectively in pure and mixed orchards. In this paper we propose to use carbon sequestration calculations as an added benefit to farmers. A carbon stocking model estimation was established, based on trunk diameters of different trees. We depicted two management scenarios based on fruits production and carbon sequestration incomes: a low value scenario, using mean fruit production, and a high valuable scenario based on the hypothesis that all trees reached its potential maximum. Since under dry-farming systems fruit production irregularity is still a pendent problem, mixed orchards may offer a potential higher revenue, while maintaining higher crop diversification and whole biodiversity. C sequestration benefit, as here we purpose, may represent 125–300 % of income, respectively under low or high valuable scenario. Thus, CO2 equivalent is a novel ecological economic incentive that may potentiate a new income for farmers while assuring carob ecosystem services.

Differentiation in populations of the apple scab fungusVenturia inaequalison cultivars in a mixed orchard remain over time

The ascomyceteVenturia inaequaliscauses annual epidemics of apple scab worldwide. Scab development is reduced in mixed cultivar orchards compared with monocultures. In order to use mixtures in commercial production, how the population of scab changes in a mixed orchard needs to be understood, together with how likely a super race, with virulence factors overcoming multiple resistance factors in the mixed orchard, is to emerge and become dominant. This study used simple sequence repeat (SSR) markers to investigate the temporal change of scab populations in two mixed cultivar orchards in theUKto infer the likelihood of emergence of a scab super race. There were no significant differences between the populations at the two sampling times (6 or 7 years apart) in either of the two mixed orchards. In one of the orchards, apple scab populations on different cultivars were significantly different and the differences did not diminish over time. These results suggest that it is not inevitable that a super race ofV. inaequaliswill become dominant during the lifetime of a commercial apple orchard.

Impact of abiotic factor changes in blowfly, Achoetandrus rufifacies (Diptera: Calliphoridae), in northern Thailand

Understanding how medically important flies respond to abiotic factor changes is necessary for predicting their population dynamics. In this study, we investigated the geographical distribution of the medically important blowfly, Achoetandrus rufifacies (Macquart) (Diptera: Calliphoridae), and ascertained the response to climatic and physio-environmental factors in Chiang Mai, northern Thailand. Adult fly surveys were carried out every 2 weeks from May 2009 to May 2010 at 18 systematically randomized study sites in three districts of Chiang Mai province (Mueang Chiang Mai, Mae Rim, and Hang Dong), using reconstructable funnel traps with 1-day tainted beef offal as bait. During the study period, 8,861 adult A. rufifacies were captured, with peak densities being observed at the end of winter (i.e., late February) and throughout most of the summer (May to March). Population density had a weak but significant (α = 0.05) positive correlation with temperature (r = 0.329) and light intensity (r = 0.231), and a weak but significant (α = 0.05) negative correlation with relative humidity (r = -0.236). From the six ecological land use types (disturbed mixed deciduous forest, mixed deciduous forest, mixed orchard, lowland village, city town, and paddy field), greater fly densities were observed generally in the disturbed mixed deciduous forest and lowland village, but not in the paddy fields. In conclusion, A. rufifacies are abundant from the end of winter and throughout most of the summer in northern Thailand, with population density being weakly positively correlated with temperature and light intensity, but weakly negatively correlated with relative humidity. The greatest densities of this fly species were collected in disturbed mixed deciduous forest and lowland village land uses. The prediction of annual and season specific distributions of A. rufifacies were provided in each season and all-year patterns using a co-kriging approach (ArcGIS9.2).

Variation in reptile community composition across different plantation types in south-eastern Nigeria

Despite many studies of reptile community composition in Africa, no studies document the variation of reptile assemblages across different plantation types. Here, we document the community composition (richness, taxonomic composition, dominance, evenness) in relation to seasonality in eight different plantation types (from cassava-yam to banana-plantain, and from cacao to mixed orchards), and at three distinct study areas in the River Niger Delta of southern Nigeria. Our study showed that the community composition of reptiles did not differ significantly across plantation types in terms of species diversity and richness during the wet season, but it did so during the dry season (possibly as a consequence of survey effects). A few highly dominant lizard species (Agama agama and Trachylepis affinis) constituted the great majority of the specimens encountered during field work. Some snake species, although usually not very abundant (in terms of relative number) were observed in nearly all sites. Typical forest specialists may enter plantations, but they were never abundant there. Tortoises did not occur in any plantations. Diversity indices and multivariate sets of analyses revealed minor differences among study areas and across plantation types in terms of community composition patterns. However, some types of monoculture plantations had higher dominance and lower evenness values than mixed orchards (= poly-culture farms), showing that monocultures provided least quality habitats for reptile communities than poly-culture farms, favoring few species due to the relatively homogeneous niche availability. Overall, a clear process of biotic homogenization, with increases in dominance, was clearly observed at all sites.

不同生境中橘小实蝇种群动态及密度的差异

Although different researches related to the population dynamics of orient fruit fly [Bactrocera dorsalis( Hendel) ]have already been conducted by many Chinese scholars,the systematic researches related to the population dynamics of B. dorsalis in different habitats have not yet been conducted. In order to reveal the effect of different habitats on the population dynamic of B. dorsalis,the population dynamics of B. dorsalis was monitored by using sex induction agents during 2008—2009 in each monitoring point in Fuzhou,Fujian,China. The study objects are displayed as follows. The first one is population dynamics and density of B. dorsalis in different orchards,including guava,carambola,grape,luffa, cucumber citrus,grapefuit and mixture orchard. The second one is population dynamics and density in orchard and its surroundings jungles. The third one is population dynamics and density in different geographical environment in orchard, including ridge and valley,along river and not. And the last one is population dynamics and density in city and countryside. The result shows,first,that the population of B. dorsalis reaches peak when the fruit ripening in each type of orchard. Second,the population density in mixed orchard is obviously higher than the orchards of single species. Third,the population density in orchard was higher than surrounding jungles during the fruit ripening while the case was contrary to former after the fruit ripening in the orchard. Forth,the population level in valley was higher than ridge while the number along river was higher than that not along river. Fifth,the population period in city subdivision is earlier than in countryside and the population density in city is also higher than in countryside. Last,some useful and effective methods for improving control of this pest were also proposed,and drawbacks of this study and the future researches were presented. Based on our results,we suggest,first,that trying to avoid mixed cultivation with all kind of fruits in the agricultural production because of the population density in the orchard of single species is much lower than mixed orchard. Second,the field microclimate should be taken into account in pest forecasting and prevention. Third,the population changing of B. dorsalis in city should be emphasized by government and quarantine department. Because the population period in city subdivision is earlier than in countryside and the former population density is also higher than later. Next,based on the limitations of this study,some suggestions for further research are presented. Insufficient number of monitoring points is the mainly limitation in this study. For example,space-time dynamic characteristic between city subdivision and countryside has not yet been reflected because of insufficient number of monitoring points. So the characteristic of space-time dynamics between city and countryside be done in future research. Moreover,the cause of the difference of B. dorsalis populations in different habitats will be revealed in future study,especially the reasons of the difference of B. dorsalis populations in different orchards,the causes of the population dynamics between orchard and its surrounding jungles and the reasons of population dynamics between city and countryside.

Occurrence of fruit flies (Diptera: Tephritidae) in a mixed mango orchard in the city of Presidente Prudente, SP, Brazil

The objective of this research was to determine the population dynamics and the diversity of fruit flies (Te­ phritidae) in a mixed orchard containing the mango (Mangifera indica) cultivars Haden, Tommy Atkins and Palmer, at the town of Presidente Prudente town, SP, Brazil. The population dynamics of fruit flies was measured from November 2005 to December 2007 through; weekly samplings of the adult insects, using yellow-bottomed McPhail traps baited with hydrolyzed protein. A total of 65,956 Tephritidae specimens was collected in nine traps, of which 2,788 were Anastrepha spp. (4.23%) and 63,168 Ceratitis capitata (95.77%). A total of 1,229 female specimens of Anastrepha was captured, of which 91.7% were A. obliqua, 3.3% A. fraterculus, 1.4% A. sororcula, 1.0% A. pseudoparalella and 0.7% A. striata. The remaining consisted of A. barbiellinii, A. daciformi, A. haywardi, A. zenildae, A. leptozona and A. montei. Ceratitis capitata and A. obliqua were the dominant species. In general, the highest densities of fruit flies occurred during the fruit-ripening period (from November to March), which is characterized by increased rainfall levels and high temperatures.

Population variation of apple scab (Venturia inaequalis) within mixed orchards in the UK

Apple scab, caused by Venturia inaequalis, is one of the most important apple diseases worldwide. To investigate between- and within-orchard fungal variability, 212 isolates were sampled from two mixed orchards, one of 10 years of age and the other of 45 years of age, in the UK and genotyped with AFLP and SSR markers. Populations of isolates from the two orchards did not differ significantly in terms of allele frequencies at the screened AFLP and SSR loci. However, groups of isolates from individual cultivars differed significantly within each orchard and there were also significant differences between groups of isolates from individual trees of the same cultivar in the same orchard. These differences were less pronounced in the younger mixed orchard than in the older one. The existence of tree-to-tree fungal variability indicates a possible role for conidia as a source of primary inoculum. Non-random mating may be one of the factors causing the significant differences among fungal populations from different cultivars. These results suggest that apparently ‘susceptible’ cultivars have different background genetic resistance factors, which can be exploited for disease management in mixtures.

Distribution and incidence of apple powdery mildew in a mixed cultavar orchards and relationship to disease severity

Distribution and incidence of apple powdery mildew in a mixed cultavar orchards and relationship to disease severity

Do climatic and physical factors affect populations of the blow fly Chrysomya megacephala and house fly Musca domestica?

The blow fly, Chrysomya megacephala (Fabricius), and house fly, Musca domestica L., are medically and forensically important flies. The population dynamic of these flies is essential for both control and forensical aspects. The aim of this study was to investigate the climatic and physical factors affecting the population trend of both species in Chiang Mai province, northern Thailand, using the Geographic Information System (GIS). Based on systematic random sampling, 18 study sites were selected in three districts (Mueang Chiang Mai, Mae Rim, and Hang Dong). Six land use types were involved in the study sites, i.e., disturbed mixed deciduous, mixed deciduous forest, mixed orchard, lowland village, city, and paddy field. Adult flies were sampled every 2 weeks using an in-house prototype reconstructable funnel trap. Two types of bait were used--one with fresh beef viscera for luring M. domestica and the other with 1-day tainted beef viscera for luring C. megacephala. Collections were conducted from May 2009 to May 2010, and analysis of climatic factors (temperature, relative humidity, and light intensity) was carried out. Correlation bivariate analysis was performed initially to determine the relationship between climatic factors and the number of flies. Consequently, an ordinary co-kriging approach, in ArcGIS 9.2, was performed to predict the spatial distribution of flies with land use and climatic factors as co-variables. A total of 63,158 flies were captured, with C. megacephala being the most common species collected (68.37%), while only 1.3% were M. domestica, thus proving that C. megacephala was the most abundant species in several land use types. A significantly higher number of females than males was found in both species. Fly populations can be collected throughout most of the year with a peak in late summer, which shows a positive relation to temperature but negative correlation with relative humidity. C. megacephala was predicted to be abundant in every land use type, from lowland to forested areas, while the density of house fly was association with altitude and land use types.

Preliminary inventory of fruit fly species (Diptera, Tephritidae) in mango orchards in the Niayes region, Senegal, in 2004

Introduction. Knowledge of tephritid diversity in Senegal was poor before 2004, so PIP-COLEACP and CIRAD, in collaboration with Ceres-DPV, carried out, in 2004, trapping for preliminary detection of fruit flies in six orchards in the Niayes zone. Materials and methods. We selected three mixed mango orchards and three homogeneous mango orchards in this zone. In each orchard, we used three attractants: Terpinyl acetate (Ter), Trimedlure (Tri) and Torula (Tor). Traps were serviced weekly. Results. We captured 77 642 fruit flies in more than 4 months including mango season; they were represented by 18 identified fly species, including ten Ceratitis, six Dacus and two Bactrocera species. Two very serious pests were identified with the confirmation of Bactrocera cucurbitae (Coquillett) for cucurbit crops and the detection of B. invadens Drew Tsuruta & White for fruit crops. The two most abundant species of Ceratitis were C. cosyra and C. silvestrii. Discussion. We captured more fruit fly specie s in mixed mango orchards than in homogeneous mango orchards. Bactrocera invadens was also more abundant in mixed orchards, probably because of its polyphagous status. This new invasive species, B. invadens , can have many hosts in mixed mango orchards , enhancing its breeding potential. Conclusion. Effective management to deal with this alien species requires: (i) improvement of basic and applied research; (ii) an effective IPM package; (iii) an area-wide management approach; (iv) a sub-regional effort on the part of researchers, extension services, growers, exporters, farming associations and the different actors in fruit value chains (mainly mango). (Resume d'auteur)

Orchard and riparian habitats enhance ground dwelling beetle diversity in Mediterranean agro-forestry systems

The relative contribution of mixed orchard and riparian vegetation patches to local and regional diversity of Mediterranean landscapes dominated by cork-oak woodlands was tested in 2006–2007 using ground, rove and darkling beetles (Coleoptera: Carabidae, Staphylinidae, Tenebrionidae). Mixed orchard and riparian gallery habitats recorded higher values of abundance and species richness for overall beetle species, although most darkling beetle species were associated with the sclerophyllous cork-oak woodlands. Ground and rove beetle community structure changed from the orchard and riparian habitats to samples placed 100 m away into the surrounding cork-oak woodland, i.e., non-cork-oak patches enhanced beta diversity within the landscape mosaic. Analysis of ground beetle traits concerning moisture preferences revealed a higher proportion of hygrophilous species in mixed orchard and riparian gallery habitats while xerophilous species were dominant within the cork-oak woodlands. The results of this study suggested that land-use management promoting the maintenance of habitat heterogeneity enhances biodiversity conservation of important hygrophilous and xerophilous species, and subsequently the sustainable use of Mediterranean agro-forest mosaics.

EVALUATION OF PROMISING SAPOTACEAE SPECIES FOR FRUIT PRODUCTION IN MICHOACAN, MEXICO

Fruit culture in Michoacan is typified by the export-orientated crops avocado, mango, guava and lemon. However, there is a great diversity of plant families and species of tropical and subtropical fruits already cultivated in sparse and mixed small orchards. Specifically there is a high potential for different Sapotaceae family species with edible fruits. The objective of this research was to evaluate promising sapotaceae species for fruit production of the Centre-Western Michoacan considering aspects of geographical, ecophysiological, morphological, agronomic, and marketing parameters. The first stage of this study presents the evaluation of qualitative and quantitative characteristics of 117 trees of Mamey Sapote, Pouteria sapota [(Jacquin) H.E. Moore & Stearn] from 13 different locations within the three most representative production areas. Clusters analysis of data indicated three distinct Clusters. Cluster I included 31 genotypes from Nuevo Urecho and Apatzingan municipalities, with strongly branched, upright trees, elliptic and globose fruits with coarse woody skin, and smooth brightly red mesocarp with very sweet taste and low acidity. Cluster II included 34 genotypes with strongly branched, spreading trees with elliptic, globose and ovate fruits and smooth salmon mesocarp. Cluster III represented by 52 genotypes mostly from Ziracuaretiro and Apatzingan with low-branched, spreading trees, with small ovate and obovate fruits. Principal component analysis detected the variables more affecting Cluster differentiation. Those were fruit weight, fruit length, mesocarp and epicarp weight, seed weight, total soluble solids (TSS) content (°Brix), pH, fruit diameter, tree high, leaf length and width, branch architecture and fructification. These observations provide the first reported in-depth insights into the genetic diversity of mamey sapote for fruit production in Michoacan. They furnish the necessary informational framework for future studies in that region.

Acceptance of artificial nesting sites by pollinating mason bees in commercial fruit plantations (Hymenoptera, Megachilidae: mixed Osmia cornuta and O. rufa population)

During a four yeas long experiment a simple bee shelterswas found to be a propermethod to increase the size ofmixed natural populations of the early season Osmia cornuta and O. rufa under practical farm conditions. Instead of the number of pesticide applications the earliness of the flowering of the fruit species in the orchards was found to be themost important factor in the rate of acceptance of reed as nestingmediumby Osmias in the bee shelter. This relationship was negative and highly significant (r = –0.829, p<0.001). This means that much higher acceptance of artificial nestingmedia in bee shelters and consequentlymuch higher population increase of the two early seasonmason bee species can be expected in orchards with early than with late flowering fruit species. Mixed orchards or early flowering orchards surrounded by other orchards falling in bloom later consecutively may also be much favourable to mason bees because they can find continuous food (pollen) supply there for a much longer time during their period of activity than in orchards planted with a single fruit species and being apart from orchards of other fruit species.

High versus ultra-low volume spraying of a microencapsulated pheromone formulation for codling moth control in two apple cultivars

Mating disruption is the controlled release of sufficiently large quantities of insect sex pheromones into the air, using pheromone dispensers, so as to disrupt the ability of males to locate and mate with females. Current microencapsulated sprayable pheromone formulations for codling moth have limited residual activity, but applying sufficient amount of microcapsules in the canopy can enhance their disruption efficacy. For this purpose, the effect of spray volume and apple cultivar on the number of pheromone microcapsules was studied in 2006 and 2007. Sprayable pheromone was applied at a rate of 25 g a.i./ha either in high-volume (768 l water/ha) or ultra-low volume (24 l water/ha) sprays with an airblast sprayer. The low-volume application deposited significantly more microcapsules per cm2 leaf, which was particularly evident in the upper tree canopy and on the undersides of the leaves. Microcapsule retention also significantly differed between ‘Fuji’ and ‘Granny Smith’ fruits treated with low-volume application. Our results suggest that spray volume and pressure reductions can increase the number of microcapsules deposited on leaves and fruits. Varying the leaf and fruit retention characteristics of cultivars may also influence the use of sprayable pheromones in mixed cultivar orchards.

A population model for the peach fruit moth, Carposina sasakii Matsumura (Lepidoptera: Carposinidae), in a Korean orchard system

A population model for the peach fruit moth, Carposina sasakii Matsumura, was constructed to understand the population dynamics of this pest species and to develop an effective management strategy for various orchard (apple, peach, apple + peach) systems. The model was structured by the five developmental stages of C. sasakii: egg, larva, pupa, larval-cocoon (overwintering larva), and adult. The model consisted of a series of component models: (1) a bimodal spring adult emergence model, (2) an adult oviposition model, (3) stage emergence models of eggs, larvae, and pupae, (4) a larval survival rate model in fruits, (5) a larval-cocoon formation model, and (6) an insecticide effect model. Simulations using the model described the typical patterns of C. sasakii adult abundance in various orchard systems well, and was specific to the composition of host plants: three adult abundance peaks (first peak, mid-season peak, and last peak) a year with decreased peaks after the first peak in monoculture orchards of late apple, two adult peaks a year with a much higher last peak in monoculture orchards of early peach, and three adult peaks a year with much higher later peaks in mixed orchards of late apple and early peach. The average deviation between model outputs and actual records for first and second adult peak dates was 2.8 and 3.9 d, respectively, in simulations without an insecticide effect. The deviation decreased when insecticide effects were incorporated into the model. We also performed a sensitivity analysis of our model, and suggest possible applications of the model.

Notes on an Unexpected Decline of a Population ofCorallus grenadensis(Squamata: Boidae) in Grenada, West Indies

A population of the treeboa Corallus grenadensis was studied (PIT-tagged) at Pearls, Grenada for two years (February 2002–February 2004). The site was one of mixed orchard and native trees, cultivated fields, one rustic house, and a well maintained trail. It became apparent that the population was in sharp decline in June 2004, and Hurricane Ivan drastically altered the site shortly thereafter (September, 2004). Subsequent searches over the next five years yielded no adult boas, and only a small number of young-of-the-year or yearling boas. As Hurricane Ivan hit after the decline, it cannot be identified as the proximate cause. Rather, as C. grenadensis is an edge species, we suggest that a decline in human activity (overgrown trail thereby reducing edge habitat) at the study site may have been the major contributor to the decline. Although treeboas, in general, may not be as common on Grenada as they were 100–150 years ago (or 5–20 years ago), it is still possible to encounter them on virtually any night in a wide variety of habitats.

Virulence characteristics of apple scab (Venturia inaequalis) isolates from monoculture and mixed orchards

Isolates of Venturia inaequalis were sampled from monoculture and mixed orchards of three apple cultivars: Bramley, Cox and Worcester. In addition, single‐ascospore progeny isolates were obtained from three crosses between pairs of isolates originating from the three cultivars in monoculture orchards. These field isolates and single‐ascospore progenies were inoculated onto each of the three cultivars in a glasshouse. The patterns of infection showed that all three cultivars, commonly regarded as susceptible to scab, contained some specific resistance factors and that scab isolates from both mixed and monoculture orchards appeared to have co‐evolved with cultivars. A much higher proportion of isolates from cv. Worcester in the mixed orchard were unable to infect any of the three cultivars than isolates from any other combination of cultivar and orchard type, but there was no other difference between isolates from mixed vs. monoculture orchards. Many isolates could infect both Bramley and Cox, or Cox and Worcester; but only a single isolate could infect both Bramley and Worcester. Results from the testing of 61 single‐ascospore progeny isolates suggested that virulence towards Bramley, Cox and Worcester was controlled by at least one, two and three factors, respectively. Moreover, the exact nature of the interactions between these factors in determining virulence depended on the particular pair of isolates concerned.