Use of stomatal index as a marker to screen backcross populations of two wild potato species segregating for freezing tolerance

The purpose of this study was to investigate differences in stomatal index among backcross progeny ofSolanum commersonii (freezing tolerant) andSolanum cardiophyllum (freezing sensitive) to assess the feasibility of using this trait as a marker for screeningSolanum populations for freezing tolerance. Measurements were taken on three terminal fully-expanded leaflets per genotype by completing microscopic examination of epidermal impressions made in partially dissolved cellophane tape. Freezing tolerance was estimated in parallel studies on the same plant material. Values of SI were significantly greater (Fisher T-test, 0.05) for theS. cmm. group (parent + backcross progeny) compared with theS. cph. group. Stomatal index of the F₁ was significantly greater than SI ofS. cph. parents and similar toS. cmm. parents. Values of SI for both backcross progenies were greater than parental values. Non-acclimated relative freezing tolerance values were in the following order:S. cmm. parents >S. cmm. backcrosses > F₁ >S. cph. back-crosses >S. cph. parents. Stomatal index values followed a similar pattern with the exceptionS. cmm. backcross >S. cmm. parents. These data suggest: a) increased SI is inherited as a dominant trait, b) SI may be a useful screening marker in breeding programs interested in improving freezing tolerance.