Interaction of Brassicaceous Seed Meal and Apple Rootstock on Recovery of Pythium spp. and Pratylenchus penetrans from Roots Grown in Replant Soils

Abstract

Pythium spp. and Pratylenchus penetrans are significant components of the diverse pathogen complex that incites apple replant disease in Washington State. The structure of the Pythium population differs among orchard soils but is composed of multiple pathogenic species. Studies were conducted to determine the effect of brassicaceous seed meals and apple rootstock on the activity and composition of these pathogen populations. Brassicaceous seed meals differed in capacity to suppress Pythium numbers and apple root infection, as well as differentially transformed composition of the population recovered from apple roots. Brassica juncea seed meal (SM) was the sole seed meal examined to suppress Pythium numbers and root infection; however, a persisting population was always detected in which Pythium irregulare existed as the dominant or co-dominant species. In general, the Geneva series rootstocks were less susceptible to root infection by native populations of Pythium, whereas M26, MM106, and MM111 were highly susceptible. Apple rootstocks from the Geneva series consistently supported lower populations of P. penetrans than did Malling or Malling-Merton rootstocks. B. juncea SM was superior to Brassica napus SM or Sinapis alba SM in suppressing lesion nematode populations. Significant rootstock × seed meal interaction was detected, and nematode suppression in response to B. napus or S. alba SM was only observed when used in concert with a tolerant rootstock, while B. juncea SM suppressed lesion nematode root populations irrespective of rootstock. These findings demonstrate that utilization of brassicaceous seed meal amendments for replant disease suppression must employ an appropriate rootstock in order to achieve optimal disease control.

Root Dynamics of Peach Replant Tolerant and Susceptible Rootstocks in Soilswith Different Cropping History

“…In our study, the significantly higher risk of fine roots becoming brown in the replant site compared to the non-replant site could be the result of damage to the epidermal and cortical tissue of root tips colonized by replant pathogens, which has previously been reported in other replant studies [10,56]. Rootstock differences in rates of browning in the replant site (Figure 3), could be associated with lower population of pathogens in roots of tolerant rootstocks, as reported in previous studies in apple replant disease [11,57,58].…”

Brassica juncea seed meal particle size influences chemistry but not soil biology-based suppression of individual agents inciting apple replant disease

“…and P. penetrans in orchard soils (Mazzola et al , 2009). However, under the conditions employed in these previous studies, the association of elevated AITC with enhanced disease suppression was pathogen dependent.…”

“…Among the Brassicaceae seed meals studied in this laboratory (Mazzola et al 2009;Mazzola and Brown 2010), only B. juncea SM has demonstrated prolonged activity toward P. penetrans and Pythium spp., and control is obtained in response to AITC generation. Therefore, assays were conducted in GC orchard soil to determine the effect of B. juncea SM particle size on suppression of these agents.…”

“…Coarse or fine B. juncea SM was incorporated into soil from a commercial apple (GC) orchard located near Manson, WA at a rate of 0.3% (wt/wt). Characteristics of soils from this orchard were previously described (Mazzola 1998;Mazzola et al 2009). For each SM particle size treatment, 250 g treated soil samples were placed in 0.946-l mason jars, with three replicate jars per treatment.…”

Selected Pacific Northwest Crops as Hosts of Pratylenchus neglectus and P. thornei

“…Even some biofumigant greenmanure crops such as mustard and sorghum (Sorghum bicolor (L.) Moench) are capable of increasing the density of Pratylenchus spp. in roots and soil before the green foliage is macerated and incorporated into the soil, whereupon disrupted plant cells release toxic products that expedite a decline in the number of nematodes remaining in soil (9,20,28,29). If those same crops are grown to maturity for extraction of oil from seed, as almost always occurs in rainfed low-precipitation areas of the PNW, the Pratylenchus spp.…”