Six years of physiological evaluation and performance of modern rootstock genotypes for peach production in Western Colorado

• Modern semi-dwarf peach rootstocks assessed for productivity and fruit quality in calcareous soils. • Fruit quality increased with decreasing vigor and increasing light availability. • Rootstock-manipulated light environment drives fruit quality development. • Vigor was related with gummosis incidence. • ‘Controller™ 6′ given reduced vigor profile showed good early precocity, high yields and large fruit size. In 2017, as part of a multi-state NC-140 trial, eight rootstock cultivars, budded to ‘Cresthaven’ peach scions, were planted and examined for their production potential in Western Colorado. Listed in order of declining vigor, the rootstocks included were: ‘Guardian®’, ‘Rootpac® 20′, ‘Lovell’, ‘Controller™ 8′, ‘Controller™ 6′, ‘Rootpac® 40′, ‘Controller™ 7′, and ‘MP-29′. One rootstock, ‘Controller™ 7′, was deemed unsuitable for alkaline soils, showing extreme iron chlorosis and diminutive growth and fruit size, so it was removed from the trial after the 3rd year. Six years of data showed that all remaining rootstocks, except ‘MP-29,’ had vigor profiles within 14 % of ‘Lovell’, a known standard, making them attractive candidates for use in increased density production systems. The two ‘Rootpac®’ rootstocks performed contrary to previous reports, with ‘Rootpac® 20′ the second most vigorous rootstock, and ‘Rootpac® 40′ the third least vigorous, only slightly larger than ‘Controller™ 6′. Additional physiological traits showing distinct differences between the rootstocks were yield, proleptic shoot formation, light interception, fruit size and internal fruit quality. Cumulative yield showed a strong linear relationship to vigor (as expressed as trunk cross-sectional area). However, ‘Controller™ 6′ had good early precocity and high yields given its reduced vigor profile. Gummosis occurrence was also positively associated with vigor. Both vigor and proleptic shoot formation manipulated the canopy light environment and impacted internal fruit quality profiles. Vigor limiting rootstocks had increased light availability through the canopy leading to enhanced dry matter content and soluble solids concentration. Cumulative fruit weight and size data showed that ‘Rootpac® 20′ had the heaviest and ‘Controller™ 6’ had the largest fruit size.