Susceptible day-neutral strawberry (Fragaria ×ananassa Duch.) cultivars are readily infected by Colletotrichum acutatum J.H. Simmonds during nursery propagation. The fungus infects strawberry flowers and fruit under warm, moist conditions and spreads rapidly throughout the nursery planting during repeated cycles of infection. Plants transplanted from infected nurseries into fruit-production fields have increased plant mortality and yield loss. This paper reviews practices adopted by California strawberry nurseries that reduce or eliminate sources of fungal inoculum, reduce strawberry plant susceptibility, or reduce pathogen spread in the nursery. California nurseries are currently using a combination of these practices to produce specific pathogen-free planting stock of susceptible day-neutral cultivars.
Strawberry (Fragaria × ananassa Duch.) seedlings were planted in a greenhouse at 3- to 4-week intervals and simultaneously inoculated at ages 80, 101, 129, or 157 days with either of two naturally occurring virus sources each of which contained a mottle, mild yellow edge, and crinkle virus complex. Inoculation by aphids with either virus source reduced vigor, petiole length, leaflet width, stolons per plant, and vegetative dry weight of plants in the greenhouse. The tendency of virus inoculation to reduce vigor and petiole length was inversely proportional to increasing seedling age. In the field, inoculated seedlings were also less vigorous than control seedlings. Virus source effects and seedling age interactions with virus source were not significant. Selection for virus tolerance, based on greenhouse vigor, petiole length or leaflet width measurements, increased the frequency of seedlings subsequently classified as virus-tolerant in the field in both 80- and 101-day-old seedlings. Selection based on greenhouse vigor or petiole length increased the frequency in 129-day-old seedlings. No greenhouse selection method evaluated was effective in 157-day-old seedlings.
Pedigrees of 134 North American strawberry (Fragaria × ananassa Duch.) cultivars introduced since 1960 were used to calculate 1) the genetic contribution of founding clones to these cultivars; 2) genetic relatedness among these cultivars; and 3) inbreeding coefficients of these cultivars. Fifty-three founding clones accounted for the pedigrees of these cultivars, with a mean genetic contribution ranging from <0.1% to 11%. Cultivars were clustered according to the genetic contribution into groups strongly related to geographic region of origin. Cultivars developed in California plus those derived in large part from California germplasm were a distinct cluster. The remaining cultivars divided strongly into two geographical divisions, with cultivars of a western or northern origin primarily in the first division, and cultivars of a southern or eastern origin primarily in the 2nd division. Cluster groups within each division also were related to the region of origin of cultivars. Cultivars also were clustered on the basis of Wright’s coefficient of relationship, a measure of genetic relatedness. Cluster groups from this analysis were strongly related to region of origin of cultivars, and were similar in content to groups based on genetic contributions. Inbreeding coefficients ranged from 0.0 to 0.875, but were <0.5 for all cultivars developed from cross-fertilization. Inbreeding coefficients were related partly to region of origin of the cultivars, but this relationship was probably an indirect result of unequal numbers of generations of controlled hybridization from common ancestors. For example, cultivars developed in California, which resulted from more generations of hybridization, generally had higher inbreeding coefficients. Strategies are suggested for maintaining and increasing genetic diversity of North American breeding populations.
‘Meeker’ red raspberry (Rubus idaeus L.) fruit harvested at three maturity stages [inception (IN), red ripe (RR), and processing ripe (PR)] on four harvest dates at weekly intervals were held 0, 3, 6, and 9 days at 0°C and 90-95% RH. Fruit retention strength, firmness, and titratable acidity decreased with increasing maturity, while berry weight, total anthocyanin concentration, pH, and postharvest rot incidence increased. Fruit were darker visually with increasing maturity when compared to color standards. Soluble solids differences among stages of maturity were not consistent for all harvest dates. During storage, fruit at all stages of maturity increased in pH, total anthocyanin concentration, and postharvest rot incidence, but decreased in titratable acidity and darkened visually. The rate of increase in anthocyanin concentration and visual darkening was greater for IN and RR fruit than PR fruit. Total anthocyanin concentration accounted for 85% of the variation in visual darkness. Changes in red hues during storage, and differences in red hues among stages of maturity, were not consistent for all harvests and were not related to total anthocyanin concentration. Firmness increased during storage for the first harvest date, but decreased for the remaining three harvests. Berry weight, firmness, and titratable acidity decreased for all stages of maturity with later harvest dates, while postharvest rot incidence increased. This decrease in berry weight was greater for RR fruit than IN or PR fruit. Harvest date affected pH and rate of weight loss of all maturity stages and fruit retention strength of IN and RR fruit, but not PR fruit. Total anthocyanin concentration increased with later harvest dates of PR fruit, but did not change in IN or RR fruit. Soluble solids decreased linearly with harvest date in IN and PR fruit, but changed nonlinearly in RR fruit.
‘Tillikum’ is a day-neutral (everbearing) strawberry cultivar jointly released by Wash. State Univ., Univ. of Idaho, Ore. State Univ., and the USDA. ‘Tillikum’ means “friend” in the language of the Chinook Indians. Its virus tolerance and high yields of quality fruit make it a promising candidate for home garden use in the Pacific Northwest.
BC 72-1-7, a selection from the British Columbia red raspberry (Rubus idaeus L.) breeding program, is being released as germplasm. It has a unique combination of desirable horticultural characteristics and resistance to several pests which will make it a useful parent. The selection is homozygous for gene Ag1 which confers resistance to Amphorophora agathonica Hottes, the aphid vector of raspberry mosaic virus. It is the 1st genotype described which is homozygous for the characteristic. The use of BC 72-1-7 as a parent makes it unnecessary to screen for aphid reaction, since all its seedlings will be resistant. Other useful characteristics of this selection are varying levels of resistance to several diseases including root rot, most likely caused by Phytophthora erythroseptica Pethb., postharvest fruit rot caused by Rhizopus spp., and probable resistance to pollen transmission of raspberry bushy dwarf virus (RBDV). Useful horticultural characteristics are high yield and bright red, nondarkening fruit color.
Morphological characteristics of whole red raspberry fruit (weight, density), drupelets (height, diameter, number), receptacle cavities (depth, diameter), and pits (individual weight) were measured three times in 1983 on five cultivars of red raspberry (Rubus idaeus L.) and three times in 1984 on 10 cultivars. Fruit strength, measured by compression and cohesion, was also recorded. Across all genotypes, compression and cohesion measurements were highly correlated with fruit weight, drupelet height and number, receptacle cavity depth, and individual pit weight. Drupelet height, drupelet number, receptacle cavity depth and width, and individual pit weight provided the largest component contribution to both cohesive strength and compression strength by path analysis.