Determination of Chilling and Heat Requirement of Four Apricot Cultivars of Khorasan Razavi Province

Dormancy is one of the most important stages in the life cycle of temperate plants and plants are required to exit from it with supply of chill unit. Flowering is defined with chilling and heat requirement. Owing to low chilling requirement, blooming happens too early and cold temperatures produce an important loss of yield by frost. In temperate fruits, awareness of the need buds to avoid winter frost is one of the main objectives in breeding programs. Studies concerning chilling and heat requirements are thus of special interest in these species, being very important for the choice of parents in breeding programs to create superior varieties of winter and spring frost (late flowering and resistant cold) provide. Utah is one of the most important model was introduced in 1974 by Richardson and colleagues. Effective temperature on cold storage in Utah model is 1/9-5/2. This is 6/1-9/12 in North Carolina and 8/1-9/13 in low chilling. Temperatures above 16 have negative effect on accumulation in Utah model. Later models were developed according to the Utah model that the Low chilling requirement (18) and the North Carolina (31) models are among them. Apricot (Prunus armeniaca L.) is belonging to warm temperate regions and due to the lack of compatibility and apricot spring frost in Khorasan Razavi province, the identification of varieties and genotypes with high compatibility and high thermal and cooling requirements to reduce the risk of early frost and increase production efficiency, seems important. The purpose of this study was to determine the need for chilling and heat requirement in apricot cultivars.
Material and In this research, chilling and heating requirements of four local cultivars of apricot were evaluated under field and laboratory conditions. This experiment was conducted at agricultural research station Golmakan. A factorial (two-factor) experiment was laid out in a completely randomized design with tree replications. First factor was various apricot cultivars (Noori- Dirras, Mashhad- Dirras, Shams Mashhad and Mashhad-44) and the second factor was chilling hours in five levels (0,100,300,500,700). About 45 branches of deciduous trees of each variety were collected when the temperature was below 7 °C. Finally, samples were taken in the greenhouse with an average temperature of 23° C and 16 hours of light and flowering percentage was recorded. For determination of chilling requirement in Utah, low chilling requirement and the North Carolina was performed in CU and Heat based on the degree of development hours (GDH) was calculated. GDHs average hours of temperatures between 5-5 / 4 ° C) and for any amount of time, sleep disruption and blossoming flowers will be calculated by 50% (5). Data analysis was done by JMP 8 and Excel softwares.
There were significant differences (1%) between chilling hours, cultivars and their interactions on flowering percent. .Under laboratory condition, cultivars began flowering after 100 hours in 4°C.The results showed that there was a significant difference between 500 and 700 hours of chilling requirement. Most of the flowering was related to 700 hours and the lowest one was in control.
There was a low difference in the chilling requirement. Heating requirement was 3300 growth degree hours (GDH) for Noori- Dirras and Shams Mashhad to 3379 GDH for Dirras- Mashhad and Mashhad-44 cultivars. Although little differences exist in flowering onset of cultivars, the differentiation of flowering period among cultivars was around one week. Various cultivars revealed little differences in flowering onset in locations they meet their chilling requirement. The chill units estimated by Utah model was 1588. Chill units in Low chilling model and North Carolina model was 1291 and 1331, respectively while in chill hours was about 1100. The heat units in Noori- Dirras, Shams Mashhad was about 3,300 and it were calculated 3379 for Dirras Mashhad and Mashhad-44, . The various models of chilling in the field conditions were calculated according to the Utah model. Chilling requirement by the North Carolina and Low chilling requirement models were calculated, respectively, 1331 and 1291 chill unit while in the chill hours, 1,100 hours were calculated for varieties. There was negative relationship between chill and heat requirement in flowering date.