Effect of Application Timing of Oxamyl in Nonbearing Raspberry for Pratylenchus penetrans Management

In 2012, the Washington raspberry (Rubus idaeus) industry received a special local needs (SLN) 24(c) label to apply Vydate L® (active ingredient oxamyl) to nonbearing raspberry for the management of Pratylenchus penetrans. This is a new use pattern of this nematicide for raspberry growers; therefore, research was conducted to identify the optimum spring application timing of oxamyl for the suppression of P. penetrans. Three on-farm trials in each of 2012 and 2013 were established in Washington in newly planted raspberry trials on a range of varieties. Oxamyl was applied twice in April (2013 only), May, and June, and these treatments were compared to each other as well as a nontreated control. Population densities of P. penetrans were determined in the fall and spring postoxamyl applications for at least 1.5 years. Plant vigor was also evaluated in the trials. Combined results from 2012 and 2013 trials indicated that application timing in the spring was not critical. Oxamyl application reduced root P. penetrans population densities in all six trials. Reductions in P. penetrans population densities in roots of oxamyl-treated plants, regardless of application timing, ranged from 62% to 99% of densities in nontreated controls. Phytotoxicity to newly planted raspberry was never observed in any of the trials. A nonbearing application of oxamyl is an important addition to current control methods used to manage P. penetrans in raspberry in Washington.

Impact of Pratylenchus penetrans on Establishment of Red Raspberry

The plant-parasitic nematode, Pratylenchus penetrans, is a major constraint to red raspberry (Rubus idaeus) production. To determine the impact of P. penetrans on the establishment and productivity of eight raspberry cultivars, R. niveus, and R. leucodermis, plants were grown in fumigated and nonfumigated soil. Then, soil and root populations of P. penetrans and plant productivity (vigor, cane height, biomass, and yield) were monitored over 2 years. In a separate experiment, the role that soil type plays in mediating P. penetrans populations and raspberry establishment was investigated. At 6 and 12 months after planting, population densities of P. penetrans were lower in fumigated than in nonfumigated soil; this trend continued 18 months after planting. All cultivars and R. leucodermis were found to be extremely susceptible to damage caused by P. penetrans. By the end of the experiment, yield was the most sensitive indicator of plant productivity among cultivars, with losses in nonfumigated soil ranging from 63 to 100% of those observed in fumigated soil. However, there was no difference in the productivity of R. niveus plants grown in nonfumigated versus fumigated soils. Results also indicated that the damage potential of P. penetrans was greater on sandy loam versus silt loam soils. The total plant biomass of 'Meeker' raspberry was 46% lower in a sandy loam soil containing P. penetrans compared with soil without P. penetrans; this trend was not observed consistently in a silt loam soil. Despite the fact that soil fumigation is increasingly more limited by regulations, this study shows the utility of fumigation in reducing P. penetrans populations for a sufficient period of time to ensure that newly planted raspberry seedlings can become successfully established.

Impact of Pratylenchus penetrans on Established Red Raspberry Productivity

The plant-parasitic nematode Pratylenchus penetrans is a major constraint to the production of red raspberry. To determine whether several popular raspberry cultivars in Washington State differ in susceptibility to P. penetrans and whether post-plant nematicides treatments are warranted, five independent, multiyear trials were conducted. Trials in existing plantings of 'Cascade Bounty', 'Chemainus', 'Meeker' (two trials), and 'Saanich' raspberry were established in northwest Washington. Treated plots were protected from P. penetrans by applying nematicides over a 3-year period, while nontreated plots received no nematicides. P. penetrans population densities in soil and root samples were assessed spring and fall of each year. In addition, impact of P. penetrans on raspberry yield, fruit composition, cane production, and root biomass was measured several times in each cultivar during the 3-year study. P. penetrans root population densities in nematicide-treated plots were consistently lower than those in nontreated plots at all the samplings. There were few consistent treatment differences in fine root biomass, the preferred feeding sites for P. penetrans. However, a complete root system sampling of one of the cultivars did show greater fine root biomass in treated plants compared with nontreated plants. When differences were observed aboveground, treated plants yielded less than corresponding nontreated plants, indicating that the nematicides may have been phytotoxic to some of the cultivars. This study suggests that post-plant nematicide applications are of limited benefit because, at least during the 3-year time period of this study, there were few observable benefits of protecting these raspberry cultivars from P. penetrans.

Soil Solarization as a Component of an Integrated Program for Control of Raspberry Root Rot

Field and growth chamber studies were conducted during 2000 to 2005 to determine the efficacy of soil solarization for the control of Phytophthora root rot of raspberry (PRR). The exposure time that was lethal to Phytophthora rubi cultures on V8 juice agar plates was evaluated at intervals up to 240 h and at a range of temperatures from 20 to 35°C. Colonies incubated at 20 and 25°C nearly covered the plates in 240 h, while radial growth slowed at 27°C and ceased at temperatures ≥29°C. The exposure times required to kill P. rubi were estimated to be 222 h at 29°C, 168 h at 31°C, 108 h at 33°C, and 52 h at 35°C. Previous exposure to shorter durations at temperature ≥29°C slowed growth of colonies when they later were incubated at 20°C. Field trials were established in 2000 and 2003 at three locations in Washington State to evaluate soil solarization for the management of PRR. Cumulative hours with soil temperatures >29°C at 30 cm soil depth in solarized plots exceeded 200 h in each trial. In the 2000 trial, combinations of solarization, bed shape, and amendments of gypsum were evaluated. Over the 3 years after planting PRR-susceptible raspberry 'Malahat' and 'Willamette', primocane growth and survival were greater (P < 0.05) in raised bed plots that were solarized than in solarized and nonsolarized flat bed plots or hilled bed plots with gypsum. In 2003, trials were initiated to evaluate solarization in combination with applications of mefenoxam and fosetyl-Al. In 2004, solarization increased (P < 0.05) primocane growth of 'Malahat' and 'Qualicum' raspberries at both locations compared to application of fungicides alone and nontreated control plots. At both locations in 2005, density and growth of 'Qualicum' primocanes were greatest in solarized plots, while canes in solarized and fungicide only plots of 'Malahat' were similar. Incidence of diseased canes was lowest in plots that received fungicides. Primocane survival and fruit yields were very low at both locations in the third season because of favorable conditions for PRR and plant stress in late spring. These results indicate that soil solarization can be an effective component of integrated management of PRR in the Pacific Northwest, especially when combined with raised beds and gypsum amendments.

Organellar segregation, rearrangement and recombination in protoplast fusion-derived Brassica oleracea calli

Cauliflower protoplasts were fused to determine the effect of protoplast source and pretreatment on organellar segregation in fusion products. Mitochondrial and chloroplast type were determined for over 250 calli from eight fusions between iodoacetate-treated or γ-irradiated leaf or hypocotyl protoplasts with fertile or Ogura cytoplasms. Organelles in fusion-derived calli were identified with five mitochondrial probes and one chloroplast probe. Mitochondrial and chloroplast segregation were independent but biased. Most calli had B. oleracea chloroplasts, but more calli had Ogura mitochondria than B. oleracea ones. Neither protoplast source nor pretreatment alone affected organelle segregation. However, iodoacetate treatment of hypocotyl protoplasts reduced their mitochondrial contribution to the fusion products although it did not affect chloroplast segregation. Over half of the calli had mitochondrial genomes distinct from those of either fusion partner; many of these contained the complete mitochondrial genome of one partner along with some mitochondrial DNA from the other. Out of 258 calli, 83 showed evidence of mitochondrial recombination, most commonly by formation of a novel 11-kb PstI fragment near the atp9 region.

Protoplast fusion-derived Ogura male sterile cauliflower with cold tolerance

Cauliflower (Brassica oleracea L. ssp. botrytis) protoplasts with Ogura male sterile and fertile B. oleracea cytoplasms were fused, producing plants with an array of organellar types. Plants with Ogura mitochondria were male sterile; those with B. oleracea chloroplasts were cold tolerant. In some fusions, unfused parental protoplasts were eliminated by double inactivation with iodoacetate and gamma-irradiation; in others, fused protoplasts were physically isolated by micromanipulation or by cell sorting. Double inactivation fusions produced the most plants, including many which were male sterile, female fertile, cold tolerant and diploid.

A simple, versatile feeder layer system for Brassica oleracea protoplast culture

Protoplasts from cauliflower (Brassica oleracea ssp. botrytis) and broccoli (ssp. italica) leaves and hypocotyls were successfully cultured on membrane filters over a feeder layer of cells from a B. campestris suspension culture. Cells from rice, tomato and tobacco suspensions were not as effective as the B. campestris cells. Plants were recovered from protoplasts of previously recalcitrant Brassica genotypes. Protoplasts cultured in low numbers (10-100) on the feeder layer divided and formed colonies capable of plant regeneration, as did fused protoplasts.