Factors Affecting Potato Soft‐rot Resistance to Pectolytic Erwinia Species in a Tuber‐slice Assay

Abstract

Potato‐tuber slices and small tubers of 12 cultivars were inoculated with isolates of Erwinia carotovora subsp. atroseptica (Eca), E. c. subsp. carotovora (Ecc) and E. chrysanthemi (Ech). Cultivar resistance was expressed as the mean diameter of the rotted‐tissue area. Grouping of the cultivars into classes of relatively high, intermediate or low resistance, was different after incubation in air in comparison to incubation under anaerobic conditions, and depended on the (sub‐)species of bacteria used. When compared to the effect of inoculation with different (sub‐)species, grouping of the cultivars was less affected by isolates within (sub‐)species. Cultivar grouping was hardly affected by site of inoculation, being either in the medullary tissue or in the cortex. In general, the results of experiments with either field‐grown seed tubers or glasshouse‐grown small tubers from 2 years were reproducible, except when tuber tissue was inoculated with Ech and incubated, aerobically, in which case cultivars only showed relatively small differences for resistance. Correlation coefficients between the results from slice and small‐tuber screenings were 0.71 and 0.64 for Eca and Ecc, respectively. This implies, some potential for applying the method in the early stages of potato‐breeding programmes.The results of this study show that soft‐rot resistance of clones to different pectolytic Erwinia spp. can be determined efficiently and reproducibly if the oxygen concentration during incubation is standardized.

Erwinia soft rot resistance of potato cultivars expressing antimicrobial peptide tachyplesin I

“…Tubers harvested from these plants were screened for tuber tissue resistance to Eta IPO 161 in a randomized block design under aerobic and anaerobic conditions according to the method for small tubers described by Allefs et al [2]. In short, 10 small tubers per transgenic clone or untransformed cultivar were cut twice tangentially at opposite sides and incubated overnight at 15 "C. A well, 4.0 mm deep and 5.0 mm in diameter, was pressed into the medullar tissue in which 20 ~1 1 x lo9 cfu/ml Eta was pipetted.…”

“…In short, 10 small tubers per transgenic clone or untransformed cultivar were cut twice tangentially at opposite sides and incubated overnight at 15 "C. A well, 4.0 mm deep and 5.0 mm in diameter, was pressed into the medullar tissue in which 20 ~1 1 x lo9 cfu/ml Eta was pipetted. Tubers were incubated at 20 "C for 3 days in nitrogen or 5 days in air as described [2]. After incubation, rotted tissue was scraped from the tubers and resistance expressed as the calculated mean diameter of the resulting cavity, measured at right angles.…”

The role of the seed tuber in determining partial resistance to potato blackleg caused byErwinia spp.

“…After incubation, rotted tissue was carefully removed and the diameter of the lesion measured in two directions at right angles. Experimental layout and analysis of mean lesion diameters were as described by Allefs et al, 1995. Nine experiments were carried out for studying tuber tissue resistance. Experimental details of these experiments which were numbered from 1 to 9, are presented in Table 1.…”

“…Since rotting of the mother tuber is an essential step during blackleg development [P6rombelon and Kelman, 1980], it was thought that selection for resistance to blackleg might be carried out by screening for tuber tissue resistance in the laboratory. Of the many methods published [see Allefs et al, 1995], the tuber slice inoculation method for screening of tuber tissue resistance as originally described by is one of the most extensively studied screening methods. It has been shown that for Erwinia carotovora subsp, atroseptica (Eca), E.c.…”

“…carotovora and to a lesser extent also for E. chrysanthemi (Ech), this method generates reproducible data under different experimental conditions Lapwood and Read, 1985;Wastie et al, 1988;Allefs et al, 1995]. The tests are much easier to perform than field tests, yield quantitative data and to some extent seem suitable for screening first generation tubers [Allefs et al, 1995], but as far as known from literature, the relation between the results obtained in the tuber slice test and blackleg resistance in the field has not been studied. We studied this relation by screening a range of 12 cultivars for blackleg resistance in the field on two locations in two years and by comparing the results with tuber tissue resistance of the same cultivars as determined with the tuber slice inoculation method.…”