Clonal populations regenerated from single-leaf cell protoplasts of the potato cultivar ;Russet Burbank' display a high frequency of variation for several horticultural and disease resistance characters. Observations over a period of three tuber generations suggest stable changes in tuber shape, yield, and maturity date, in photo-period requirements for flowering, and in plant morphology. Enhanced resistance to early blight (Alternaria solani) and late blight (Phytophthora infestans) diseases also regularly occurs within regenerated populations. These findings are discussed in the context of possible application to varietal improvement, particularly as they pertain to asexually propagated plants.

No abstract

Mesophyll cell protoplasts were isolated from potato (Solanum tuberosum L. cv. Russet Burbank) leaves (e.g. 2, 6, 8, 9) have been induced to reform their cell walls, undergo sustained proliferation, and ultimately redifferentiate whole plants. This feature of protoplast totipotency among the experimental plant species studied thus far suggests a viable new approach toward crop and varietal improvement (3) once similar success is achieved for species of major economic consequence.The potato, which ranks fourth among world food crops (19), has been recalcitrant in tissue culture. In only a few cases (5, 10, 14, 20) has plant regeneration been achieved from excised tissues other than shoot tips. Recently, however, there has been definite progress toward the development of an in vitro regeneration system from single cells. Upadhya (18) cultured protoplasts from potato leaves and obtained calli which differentiated roots but not shoots. Behnke (1) plated cells from dihaploid suspension cultures and reported that "small shoots" emerged in a high percentage of individual calli, although mention was not made of whether whole plants were obtained. In the present study, calli raised from single mesophyll protoplasts of potato were induced to undergo shoot formation and eventually regenerate whole plants. The developmental sequence, while dependent upon the proper balance of phytohormones, was also sensitive to numerous other constituents of the culture medium.

Sixty‐five selected clones of potato (Solanum tuberosum cv. Russet Burbank) regenerated from mesophyll protoplasts (protoclones) were analyzed for variability under field conditions. Protoclones were planted in randomized complete blocks replicated six times. During the growing season and after harvest a total of 35 characters were measured for each clone and compared with similar measurements from the parental ‘Russet Burbank’ and with another virus‐tested clone of the cultivar. Statistically significant variation was found for 22 characters, variation not amenable to statistical treatment in 4 characters, and no variation in 9 characters. Protoclones were nearly equivalent in most characters to both Russet Burbank standards. However, quantitative data showed that each protoclone differed from Russet Burbank in some trait(s). Variation ranged from a minimum of one character in three protoclones to a maximum of 17 characters in one protoclone. Differences in vine morphology, tuber yield and composition, maturity and flowering were observed. Some of the variability found should be an improvement over normal traits found in the normal cultivar. Further testing is necessary to determine both the stability of and the effect of the environment on this variability. However, the data do suggest that for potatoes, protoplast regeneration may offer a new means of generating variability of potential use for crop improvement.