During 1997-2002, studies on the physiological and biochemical changes due to powdery mildew attack in peach and nectarine cultivars and hybrids belonging to different classes of resistance had been performed at the Research Station for Fruit Tree Growing (RSFTG) Baneasa Bucharest, located in the southern part of Romania. The study was based on... disease assessments in the field and on other diagnosis criteria.
The southern part of Romania has favourable ecological conditions for growing peach and nectarine but trees have been attacked by various pathogens such as Sphaerotheca pannosa (Wallr.: Fr.) Lev. var. persicae Woronichin fungus for a long time. The presence of the pathogen causes important changes in the quantity and quality of fruits and affects the metabolism of trees.
This study was focused on several physiological and biochemical parameters such as photosynthesis and respiration intensity along with catalase activity; and changes in some biochemical compounds such as free, total and linked water content, dry matter, nitrogen and protein content, tannin levels. The aim was to find possible correlation among the above parameters and the biotic stress induced by the powdery mildew fungus calculated as attack degree (AD%).
Results showed that photosynthesis diminished significantly in the case of the attacked phenotypes, the respiration was more intense in the infected cultivars and catalase proved to be less intense in the affected plants. The total water content significantly increased in contrast to the dry matter and tannin contents, which greatly reduced in the case of resistant cultivars such as 'Victoria', Vectared 7', 'KB 11-40'. The total nitrogen and protein levels showed less influence on resistance to powdery mildew on all cultivars. All genetic material found resistant to powdery mildew is currently used in peach and nectarine breeding programs in Romania.
Further studies focused on isolation and characterization of resistance genes for powdery mildew resistance will be done in the future based on data collected during several years.
The geographic location of Bucharest area, the nature of its soil and its climate offer remarkably favourable conditions for nectarine growing, with juicy and well flavoured fruit, good for fresh consumption and processing.
The five years' investigation (1996-2000) has helped to identify some nectarine cultivars and hybrids (NJN 58, ARK... 165, ARK 139, Morton, ARK 107, Romamer I, ARK 125, Firebrite) with exceptional fruit quality (dry matter content, titratable acidity, vitamin C content, overall sugar, and amount of pectic substances).
Dry matter content varied over the three years from 8.3 to 18.5% (NJN 68), meanwhile titratable acidity varied between 0.26 and 1.08% (Romamer I). Sugar / acidity ratio was within the limits of 8.6 and 36.5 (Nectared 7). Nectarines have high vitamin C content, over 10 mg/100g (Fairlane, NJN 67, Regina, Harko), glucides were found in Firebrite, Romamer I varieties and NJN 21, CIR1T127, HFSR3P4, HNA hybrids.
Some cultivars have been recommended for planting in this southern area of Romania (Crimsongold, ARK 125, Harko, Hardyred, ARK 134), others used as quality genitors (ARK 85, Nectared 7, NJN 21, ARK 21, ARK 134, Fantasia) in breeding projects.
In the laboratory of Conserve-technology in the Research Institute for Fruit Growing, Company of Public Utility, Cegléd, 6 sour cherry, 6 apricot, 5 peach and nectarine, 6 plum and 4 Japanese plum varieties (canned fruit, juice, dried fruit, deep frozen). The products were evaluated by organoleptic methods on a scale of 1-5 steps. The varietie...s receiving at least 4 points were listed (in brackets also the respective product was indicated): `Kántorjánosi' sour cherry (for all the three purposes), '13' variety candidate (canned and deep frozen), 'T' var. cand., (canned, deep frozen), 'Érdi bőtermő' (dried fruit), 'R' var. cand. (deep frozen); ‘Ceglédi arany', 'Ceglédi bíborkajszi', 'Magyar kajszi"C. 235' (fibrous juice); `Babygold 5', 'Redhaven' peaches, and 'Caldesi 2000' nectarine (canned); 'Stanley' plum (canned), 'Besztercei Bt, 2' (deep frozen).
Researches concerning the selection of some nectarine varieties as genitors for the breeding program in Romania
The peach is though considered to be a self fertile fruit species, also some self sterile and male sterile varieties have been registered. The latter type seems to be frequently met in Asian varieties, whereas in the USA and Europe, J. H. Hale and Flaminia are grown. The purpose of the present study was the assessment of ferti...lity relations of peaches and nectarines grown in Hungary. The authors studied, since 1974, more than 100 different peach and nectarine varieties as for fertility relations, especially their autogamous or geitonogamous fruit set on isolated, i.e. bagged flowers at bud stage, then set free after blooming finished. Isolated flowers of some varieties were also self pollinated, artificially. According to the results the varieties have been assigned to four alternative groups. Self sterile varieties in the proper sense have not been found, but partial self sterility (less than 10% fruit set), self fertility (10 to 20% fruit set) and high self fertility (more than 20% fruit set on selfed flovters) was generally met. The majority of the varieties belonged to the last two groups, nevertheless. the rate of fruit set displayed seasonal variation, the maximum was in one case 89.9%. The purposeful self (hand)pollination of the isolated flowers increased fruit set, substantially. Varieties rated as partially self-sterile are J. H. Hale and Fuzador (the former being partially male sterile too). Although in some years and some varieties, fruit set legged below 10% but according to the means the majority of nectarines are assigned to the self fertile category whereas most peach varieties, either for fresh consumption or industrial types, were highly self fertile.