Investigation of phenology and estimation of flower buds chill and heat requirements of some commercial almond cultivars using different models

Almonds are high in antioxidants, vitamin E, protein, and fiber. This nutrient-rich nut is an excellent addition to any diet since it is a versatile ingredient linked to several health benefits. The development of communications have led to a wider cultivation of temperate fruits, cultivars being selected and grown in different environmental conditions. This situation has increased the risks derived from the incomplete breaking of dormancy, and encouraged studies concerning the chilling and heat requirements of fruit cultivars for breaking dormancy and flowering. Estimating chilling and heat requirements of flower buds in fruit trees is important due to predicting flowering time for appropriate site selection to escape spring frost damage.

In order to investigate the chill and heat requirements of commercial almond cultivars, a factorial experiment was planned and implemented in a completely randomized design with 3 replications in Shahrekord university lab (in 2017). The first factor included commercial almond cultivars in five levels (Mamaei, Rabi, Sefid, Shahroud 7, and Shahroud 12) and the second factor included chilling in seven levels (100, 200, 300, 400, 500, 600, and 700 hours at 4-7 °C). As soon as dormancy was induced in the buds of each cultivar, 75 branches were prepared and transferred to a refrigerator with a temperature of 4 to 7 ° C to determine the chilling requirement. The samples were taken out of the refrigerator and placed in water and sucrose solution in the greenhouse environment, and the flowering status of flower buds was examined.

The results illustrated that the chill and heat requirements of Sefid and Mamaei cultivars were lower than average requirements of all cultivars in this respect. Furthermore, these two cultivars had the lower chill and heat requirements than other cultivars. Also, Sefid cultivar needed 170 hours of chill requirements and 5886 growing degree hours’ heat and Mamaei cultivar needed 170 hours of chill and 7707 growing degree hours’ heat. Rabi cultivar had lower chill and heat requirements than the average of all cultivars, but in Shahroud 7 cultivar both of chill and heat requirements were high. Shahroud 7 cultivar needed to 220.5 hours of chill and 10958 of heat growth degree hours for blooming. On the other hand, Shahroud 12 cultivar was identified as a cultivar with high chilling requirements and low heat requirements.

The minus effects of the lack of chilling for breaking dormancy in temperate fruits, both in vegetative growth, and fruit-bearing have been proved. Chilling requirements of temperate fruit cultivars have to be fully satisfied, if dormancy breaking is to result in the desired vegetative growth, and if the fruit-bearing capacity is to be fulfilled. On the other hand, in case of low chilling requirements blooming happens too early and cold temperatures produce an important loss of yield by frost.