|Steffens, George - USDA, ARS - RETIRED|
Submitted to: Horticulture Scientia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 2, 1996
Publication Date: N/A
Interpretive Summary: Micropropagation provides a new method for propagating apple trees with their own roots rather than requiring the use of a rootstock. Because the propagation method is new and different, trees produced in this way must be evaluated in the field for many years to make certain that they will maintain the characteristics of the particular variety and will be productive. Micropropagated trees were planted in the orchard at Beltsville as soon as possible after they were produced. The trees were measured for growth every year and flowering and fruit yield was measured annually after they had started. Micropropagated trees varied by cultivar in the amount of growth produced, the age at which flowering started, the amount of fruit produced and the year-to-year consistency of fruit production. Only one of the 25 varieties tested showed any variation from normal in tree characteristics. Varieties that could be used as micropropagated trees in commercial orchards were identified as were some varieties that would not be suitable when propagated in this way. The data obtained will assist scientists in developing productions systems using micropropagated trees.
Technical Abstract: Micropropagated apple (Malus domestica Borkh.) trees of 20 cultivars, including both standard and spur-type growth habits, were grown for up to 14 years and measurements were taken annually of size (trunk cross-sectional area), flowering and yield. For three consecutive years (1988-1990), photosynthesis, stomatal conductance, chlorophyll content, leaf area and specific leaf weight were measured on three trees of each of 16 of these cultivars on at least three dates per year. The data show differences among the cultivars in vegetative vigor, age at which flowering began, fruit yields, photosynthesis, stomatal conductance and chlorophyll content. Trees did not display intraclonal variation except for one spur type, 'Redspur Delicious' in which the spur characteristic was variable from tree to tree. The results are useful in assessing the potential for using micropropagated apple trees.