Edina MENDELNÉ PÁSZTI1 – Ákos MENDEL1
1Hungarian University of Agricultural- and Life Sciences, Institute of Horticultural Sciences, 2700 Cegléd, Szolnoki st. 52. Mendelne.Paszti.Edina@uni-mate.hu, Mendel.Akos@uni-mate.hu
Abstract
Apricots have been qualified as Hungarikum in 2018. Their extremely low ecological adaptation immensely affects their utility and production. From the national agricultural research point of view, it is crucial to have reliable origin and quality of plant materials to be able to carry out proper analysis, which would support the achievement of crossbreeding. The sustainable cultivation of apricots is greatly threatened by crop fluctuations due to frost damage during flowering, which cause difficulties for farmers every year. For the past 50 years the use of rootstock and varieties as well as the production system have changed. The fruit trees are now facing new challenges from ecological and plant pathological aspect. Our aims are to examine which varieties provide greater crop safety as well as which varieties mean a higher risk. In order to improve our cultivars these results will be used during breeding. Characteristics that are not related to the quality and quantity can be examined preliminarily. With this innovative approach, the time and resources required for breeding new apricot varieties can be significantly reduced.
Keywords: Apricot, Breeding, Cegléd, Frost damage
Introduction
One of the main dangers of apricot cultivation in Hungary is the frequent winter and spring frost damage. In some places, fruits can be fully harvested only once every 3-4 years. Breeding of woody plants is a very slow process, since to turn to fruit period can take 4-5 years. Numerous researches have previously focused on a deeper understanding of the frost tolerance of apricot flower buds, but all of them were qualitative (Szalay et al.; 2016; Szalay et al. 2019). By these studies it was possible to determine the changes in the frost tolerance of each variety over time, and the differences between the years.
During the winter, at certain intervals branch samples were collected from the trees of the varieties in question, which were frozen at different temperatures to determine the degree of frost tolerance. According to the studies, the frost tolerance of each apricot variety develops differently during the dormant period, thus they also bear various degrees of tolerance against spring frosts. Winter and late winter temperatures greatly influence the development of dormancy, affecting the time of flowering. From these studies it can be shown that the Hungarian-bred apricot cultivars (especially the newer selections) have better frost tolerance than the Italian or Spanish cultivars.
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In Serbia, a research team of Tomo Milošević conducted similar researches at Čačak. An artificial freezing method was also used to model changes in frost tolerance over time. In addition to Serbian apricot cultivars, Hungarian apricot cultivars were also included in their studies, which show that in contrast to cultivars with Mediterranean origin, the varieties selected for the continental climate have better frost tolerance (Glišić et al.
2019).
Even though late spring frosts are less common in Italy, since it has a Mediterranean climate, yet they are studying flowering buds’ chilling tolerance. The requirement of cold temperature of apricot varieties and their different developmental dynamics necessitate call for researches in the case of varieties grown in warmer climates. Moreover, varieties with better frost tolerance can be grown more economically in areas that are less prone to frost. When studying Italian-bred apricot cultivars, Viti and colleagues found that although they have lower cold requirements and are less resistant to frost than continental varieties, there are also significant differences between them. Among them, those who perform better can be highlighted, and varieties that are more resistant to late spring frosts can be produced with their help. Their studies also included the inheritance of frost tolerance and cold demand in offspring populations. Better frost tolerance was also detected among the offspring (Viti et al. 2010a; Viti et al. 2010b).
Ruiz et al. (2007) found that the difference between the winter cold demand of apricot cultivars can be up to 100% (596–1266 h). In the study of several apricot cultivars a method was developed, which could be used to detect more accurately the cold demand of each genotype. Their measurements were based on the dynamics of weight gain of flower buds, so they were able to eliminate differences between crop years.
The large-scale summary work of Sánchez-Pérez et al. (2014) includes the genes available for flowering time in stone fruit species (apricot, peach, plum, cherry, almond, and wild Prunus species). In the experiments of Balogh et al. (2019), genes belonging to the CBF and DAM gene families (ParCBF1, ParDAM5, ParDAM6) were identified that are responsible for maintaining the dormant state of apricots. These genes are also found in apricot, peach, cherry, almond, and wild Prunus species, and their sequences show a high degree of similarity. Based on this, the markers associated with the studied genes can most likely to be applied to other cultivated stone fruit species.
Similar CBF genes have been described in studies of Prunus mume as well as grape varieties (Xiao et al. 2006; Guo et al. 2014).
Ji-hao et al. (2010) identified the sHSP gene family in Prunus salicina species, which not only affects the freezing of buds and flowers, but it also is reduces responses to summer heat stress. Members of this gene family are also found in all temperate fruit species, thus the use of markers linked to members of this gene family may also aid in the identification of heat shock resistant lines in addition to frost tolerance testing.
Bielenberg et al. (2015) examined peach populations and successfully identified QTLs (qCR1, qCR2, qCR4a, qCR4b, qCR5a, qCR5b, qCR8) that are highly inherited in association with cold demand and bud dormancy. Using the molecular markers closest to these sites, early and late flowering lines could be distinguished. With these molecular
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techniques, as well as by examining the frost tolerance of flower buds, a method can be implemented to safely determine the frost tolerance of a variety or breeding line, even in the seedling population.
Materials and methods
Similarly to the previous decades, bud-frost damage study in the apricot orchards of the MATE Institute of Horticultural Sciences at Cegléd was conducted this year as well. For years, we have been testing 30-40 varieties in February and March. In most cases, the whole bud does not freeze, only the pistil suffers from frost damage (Fig.1). In the case of apricots even though the flowers are blooming, they are not fertile.
The region has a temperate, continental climate with a semi-arid microclimate. This area is not optimal for apricot growing, however the one third of Hungarian apricot orchards are situated in similar locations. The altitude is 96 meters above see-level. The surface is plain with some local differences (by 1-2 meters). The experimental orchard can be approached on concrete road, and has a fence around it.
The orchard was planted in spring of 2000 in 5*8 m spacing (5 meters between the trees and 8 meters between the rows), living mulch between the rows were sod with grass at the same autumn. The irrigation is not resolved yet. Pruning is performed once a year, such as foliar fertilization. Plant protection is outstandingly respected. Examining 100-100 buds per variety, we can calculate the percentage of flowers unsuitable for fertilization. This paper is based on 36 examined lines (27 cultivars a,d 9 hybrids) in three following years (2017-2019). Every numeral is a mean of three measurements.
Weather data is collected by a MilliMet-2 weather station (Boreas Kft) located 30 meters apart from the orchard, and processed with InterMet3 program.
Results
At spring of 2017, the meantime of blooming endured from 24th of March to 30th in the apricot orchards of the Research Station of Cegléd. During the two-week period before the start of blooming, the temperature lowered below freezing point only at dawn of 15th of March (-0,6°C). In the blooming period, dawn of 27th of March brought -1,2 °C, otherwise, no frosts occurred.
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1. Figure. Cross-sectional view of flower buds in early march A: No damaged organ; B: Frost-damaged pistil ; C: Entire bud damaged
As we can see on 1. table, different cultivars and hybrids have different tolerance against frosts in blooming time. Frost damage at the year 2017 was 20,1% in the average of the lines. It is not the worst of the studied years, but enough to detect variance. Varieties that shown the best tolerance in this year are Bergeron (2%), Magyar kajszi C. 235 (2%), Ceglédi óriás (2%), followed by Ceglédi Piroska (4%), Mandulakajszi (4%), H-II 45/45 (5%), Sun Glo (5%) and Veecot (6%). The biggest damage occurred at the H-II 10/14 hybrid, Ananászkajszi and Tom Cot (71%, 32% and 32% respectively).
In 2018 the blooming period prolonged due to the cold spring. It lasted from 22nd of March to 10th of April. During the weeks preceding the blooming the weather was very variable. First week of March was bitter, frosty days brought -11°C, -8,2°C, -9°C temperatures. At the second week, no frosts were noticed. Therefore, the flower buds rose quickly, and the red bud stage developed. At the following two weeks, the freezing weather returned, harming the far-gone buds. After the blooming period, there also were several morning frosts, hence the fruit-setting was poor at almost every cultivar.
The colds of March at 2018 generated 48,6% damage in great total. The best variety of 2018 was the worst of 2017: H-II 10/14 shown no damage at all (0%). Ceglédi bájos (13%), Ceglédi zamatos (13%) and Tengeribarack C.580 (18%) was the following ranking. Some cultivars beared extremely high frost damage in this year, such as Ceglédi bíborkajszi (92,5%), Rózsakajszi (87%), Veecot (84%) and H-II 25/62 (78,5%).
At spring of 2019, the meantime of blooming of apricots endured from 14th of March to 24th. During this period no frost were observable, but at 25th and 26th the temperature lowered below freezing point. These two frosts had only a minor effect on fruit-setting.
A B C
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1. table. Stacked frost damage of flower buds. Damaged buds shown in percentiles at the investigated lines.
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