Temporal variations in flowering of 'Honeycrisp' apple grafted on eight different rootstocks

Malus domestica is one of the world's most important deciduous fruit trees. Over a four-year period (2017-2020), temporal variations in flowering were evaluated in 'Honeycrisp' apple trees on eight rootstocks (G.30, G.969, G.202, G.41, G.11, M.9T337, M.26 EMLA and V.6) planted in 2014 in Chihuahua, México. Among the variables evaluated were the probability of late-spring frost, winter chill units, growing degree days, flowering period, foliar nutrient concentrations, trunk cross-sectional area, number and weight of fruit per tree, and production efficiency. Significantly different chill unit accumulations occurred over the four years, with values falling between 974 and 1 415, where for the latter value, the start of flower opening was earlier, but there was a higher risk of damage by temperatures ≤ -2 °C. There was no effect of rootstock on the time of onset and end of flowering. The most productive combinations were 'Honeycrisp' on G.969, G.11 and V.6 with yield estimates of 35 300, 34 200 and 33 600 kg/ha, respectively. The commercial production of 'Honeycrisp' apple trees requires the evaluation of their agronomic performance with different rootstocks. Flowering is particularly important since this phenological stage is so closely linked to productivity and is strongly affected by variations in winter temperatures.