نوع مقاله : مقاله پژوهشی
نویسندگان
1 استادیار، پژوهشکده میوه های معتدله و سردسیری، موسسه تحقیقات علوم باغبانی، سازمان تحقیقات،آموزش و ترویج کشاورزی، کرج، ایران.
2 دانشیار، پژوهشکده میوه های معتدله و سردسیری، موسسه تحقیقات علوم باغبانی، سازمان تحقیقات،آموزش و ترویج کشاورزی، کرج، ایران.
3 استاد، پژوهشکده میوه های معتدله و سردسیری، موسسه تحقیقات علوم باغبانی، سازمان تحقیقات،آموزش و ترویج کشاورزی، کرج، ایران.
4 مربی، بخش تحقیقات علوم زراعی و باغی، مرکز تحقیقات و آموزش کشاورزی و منابع طبیعی استان آذربایجان غربی، سازمان تحقیقات،آموزش و ترویج کشاورزی، ارومیه، ایران.
چکیده
کلیدواژه‌ها
عنوان مقاله [English]
نویسندگان [English]
Developing new horticultural crops cultivars and rootstocks is possible through various breeding methods including hybridization, identification and collection of high yield and high quality native genotypes, as well as evaluating the adaptability of commercial introduced cultivars. The utilization of new cultivars and rootstocks adapted to a region’s climatic conditions plays a significant role in enhancing both the quantitative and quality attributes of crop production. The apple rootstocks breeding program in Iran started in 2005. Within this research program, in addition to assessing the adaptabilty of commercial apple rootstocks, native rootstock genotypes such as Azayesh Isfahan, Morabaei Mashhad, Gami Almasi, and Sibgol have been identified, collected and evaluated. Important characteristics for selecting apple promising rootstocks include clonal propagation ability, proper establishment in the soil, early bearing and suitable performance of grafted trees as well as resistance/tolerance to biotic and abiotic stresses such as collar and root rot, fire blight, woolly aphid, drought stress, and high lime content in the soil. Hybridization between native genotypes and commercial rootstocks is practiced in Iran’s apple rootstock breeding program. Promising apple rootstocks developed in this program will be commercially released.
Keywords: Apple, rootstock, tolerance, Phytophthora, fire blight, woolly aphid, drought stress.
Introduction
Iran is not only one of the major apple producing regions in the world, but also one of the natural habitats, centers of diversity and areas of initial apple distribution in the world (James and Aldwinckle, 1983). Therefore, so far, numerous species and cultivars of this crop have been identified and reported by botanists in Iran. The existence of this genetic diversity and dwarf varieties in ancient Iran was such that a number of ancient miniatures not only depicted the apple tree as one of the main varieties of gardens, but also clearly indicated the existence of dwarf apple varieties in this land. Although dwarf apple trees have been found in the northern forests and highlands of West Azerbaijan, Khorasan, and Isfahan provinces since ancient times. Botanists consider Iran to be one of the areas where ornamental apples, including Morabaei, Azayesh, Sib Gol, and Gamii Almasii, have originated.
Apple trees are mainly found in the form of rootstocks and scions. Rootstocks are responsible for tree establishment and water and nutrient uptake, and also have important effects on scion growth and development, fruit yield and quality, and resistance to biotic and abiotic stresses (Wang et al., 2019). To optimally utilize valuable water and soil resources, it is essential to establish high density and semi-density orchards using suitable and adapted apple rootstocks. Each country use specific rootstocks according to its climatic conditions. Europe began the commercial use of dwarf apple rootstocks relatively early. Currently, apple-producing countries in Europe mainly use clonal rootstocks.
In the Britain, France and the Netherlands, the objectives of breeding are to improve the currently used rootstocks, such as M9 and M26, with better performance in terms of production, fruit size and quality, resistance to soil-borne diseases and pests and competition with weeds for water and nutrients. When carrying out apple rootstock breeding, we must first pay attention to the horticultural characteristics (grafting compatibility, propagation ability, dwarfing, effect on scion growth, etc.). In addition, we must also consider environmental factors (temperature, irrigation, soil pH and fertility, etc.) and biological factors (viruses, bacteria, nematodes, apple woolly aphid and other destructive animals) in the planting area (Robinson et al., 2003).
Important charactristics in improving apple rootstocks: 1. Selection for rooting and clonal propagation ability. The most important characteristic of rootstocks is their ability clonal propagation. If the selected genotype is resistant/tolerant to various stresses but does not have the ability for clonal propagation, it should be screened in the first stage. 2. Selection for micropropagation ability. Micropropagation of apple plays an important role in producing healthy, disease-free plants and rapid propagation of scions and rootstocks with desirable characteristics. Successful micropropagation of apple using apical bud or branch segment culture is influenced by several internal and external factors, including plant material (such as genotype and physiological state) and laboratory conditions (such as medium components and light). 3. Selection for resistance to crown and root rot disease (Phytophthora cactorum) crown and root rot disease of apple trees, especially in areas with poor soil drainage, causes the death of quite large trees. Researchers have conducted extensive research on the evaluation and selection of disease-resistant rootstocks for effective disease management in an integrated control system. According to the Cornell University Rootstock Improvement Protocol, screening the progeny population resulting from cross-breeding in apple rootstocks for Phytophthora diseases is considered one of the most important steps in rootstock development (Fazio et al., 2022). 4. Selection for tolerance to drought stress. Investigating the response of plants to drought stress using physiological indicators has been proven in many studies. The main goals of improving apple rootstocks is tolerance to drought stress. Tolerant rootstocks can transfer drought tolerance to the cultivars grafted onto them. 5. Selection for fire blight toleranceFire blight is transmitted to the tree through rootstocks, and if the rootstock is susceptible, the disease spreads rapidly in the tree and the tree dries up.
Therefore, in apple rootstock breeding programs, fire blight resitance is considered one of the first and most important rootstock screenings criteria. 6. Selection for tolerance to apple woolly aphid appleThe apple woolly aphid is not usually controlled with pesticides because aphids often reside in bark crevices, which reduces their exposure to pesticides, and the protection provided by the waxy secretion on their bodies minimizes the effectiveness of chemical control. Today, many apple rootstock breeding programs emphasize resistance to apple woolly aphid and diseases in addition to desirable horticultural traits. 7. Selection for dwarfing and early fruiting. The evaluation of the dwarfing and the growth ability of the progeny are considered to be the most important indicators for the selection of promising clonal rootstocks (Johnson, 2000).
The best method for evaluating the dwarfing ability of rootstocks is to graft apple varieties onto them and evaluate them in the orchard. To achieve apple rootstocks with adaptabilty to soil conditions in apple growing areas, crosses between native Iranian dwarf apple genotypes (Azayesh Isfahan and Morabaei Mashhad) as maternal parents and M9, M27, and B9 rootstocks as paternal parents have been carried out from 2005 to 2008, and a population of over 4000 seedlings resulting from the crossing and open pollination of the parents reached the evaluation stage. Primary evaluation for selection of easy rooting apple rootstocks in mound bed layering condition in two stages (from2009 to 2015) was carried out.
Among 4000 hybrid and open pollinated seedlinges, 245 genotypes with high rooting ability were selected. These progenies remained for continuing screening in second phase of project included: rooting ability of hard wood cutting, in the second screening 27 genotype with high rooting ability was selected. The resultes showed that in different cross combination, progenies of Azayesh×M27, Azayesh×M9 and Azayesh open pollinated had high rooting ability, and progenies of Morabaei had low rooting. In addition to progenies of Azayesh have good characteristics as rootstock than progenies of Morabaei. Rooting type of progeny was very different, the number of deep root in open pollination progeny of native genotypes was more than commercial apple rootstocks. This characteristic is very important for drought tolerance and adaptability of rootstocks. Then the level of tolerance to biotic and abiotic stresses, including crown and root rot disease, fire blight, woolly apple aphid (Eriosoma lanigerum), drought stress tolerance, micro-propagation, and dwarfing ability of the promising genotypes were tested. It is expected that four promising apple rootstocks will be commercially released and available to apple growerds in Iran.
References
Fazio, G., Aldwinkel, H.S. and Robinson T.L. 2022. Selection of apple rootstock breeding families for Phytophthora crown rot resistance. Acta Horticulturae, 1346, pp.717-722. DOI: 10.17660/ActaHortic.2022.1346.90.
James, N.C. and Aldwinckle, H. 1983. Breeding Rootstocks. Plant Breeding Reviews, 1, pp. 295-394.
Johnson. W.C. 2000. Methods and results of screening for disease and insect apple rootstocks. The Compact Fruit Tree, 33, pp.108-111.
Robinson, T.L., Fazio, G. and Aldwinckle, H.S. 2012. December. Characteristics
and performance of four new apple rootstocks from the Cornell-USDA apple rootstock breeding program. Acta Horticulturae, 1058, pp.651-656. DOI: 10.17660/ActaHortic.2014.1058.85
Wang, Y., Li, W., Xu, X., Qiu, C., Wu, T., Wei, Q., Ma, F., and Han, Z. 2019. Progress of apple rootstock breeding and its use. Horticultural Plant Journal, 5(5), pp.183–191. DOI: 10.1016/j.hpj.2019.06.001
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