Location: Crop Improvement and Protection Research
Project Number: 2038-22000-019-029-R
Project Type: Reimbursable Cooperative Agreement
Start Date: Feb 1, 2022
End Date: Jan 31, 2023
Objective:
To address the California Strawberry Commission research priorities for: 1 – Farming without fumigants, and 2 – Management of soilborne diseases by:
1.1 Experimental assessment of susceptibility and colonization of rotation crops to M. phaseolina.
1.2. Grower field surveys to investigate susceptibility and colonization of rotation crops to M. phaseolina.
2.1 Assess Macrophomina and F.o. fragariae disinfestation on tissue fragments placed at three soil depths after fumigation with TriClor (350 lb/acre chloropicrin) and PicClor60 (350 lb/acre chloropicrin and 240 lb/acre 1,3-dichloropropene).
2.2 Assess disease severity caused by Macrophomina and F.o. fragariae after TriClor and PicClor60 broadcast treatments.
Approach:
Objective 1.1: Experiments to assess colonization of rotation and cover crops by Macrophomina phaseolina. In an M. phaseolina-infested field we will quantify the amount of the pathogen present in the soil. We will then transplant eight rotation crops in 10-plant plots with six plot replicates arranged in randomized complete block design. The crops tested will be: broccoli, broccoli raab, cauliflower, kale, iceberg lettuce, romaine lettuce, spinach and cilantro. Each crop will be grown to maturity, and any symptoms that are consistent with charcoal rot will be recorded at the end of the growing period. Then, Macrophomina will be quantified (microsclerotia per gram) from rhizosphere soil (i.e. soil in contact with the root) and fine roots. Taproots will also be assayed for the presence or absence of Macrophomina.
During the fall/winter season of each year, the Macrophomina-infested area will be planted with 16 cover crops (different than the summer season crops grown previously) and cultivated as previously described. We will assess the incidence of taproot infection for these 16 cover crops, which represent ten species in three plant families. For each crop we will assay 10 plants per block from 6 block replicates. In addition to these studies to assess infection rate, we will plant combinations of the aforementioned cover crops into 50-foot sections of 80” beds with seeding rates that are typical for these crops. Each field treatment will be established in 6 block replicates arranged in randomized complete block design. From two locations in each replicate of each treatment (i.e. 48 locations total), we will quantify soil Macrophomina populations before planting, at the time of tillage, and 8-weeks post tillage.
Objective 1.2: Grower field surveys to investigate susceptibility and colonization of rotation crops to M. phaseolina. Five fields in strawberry production with M. phaseolina disease outbreaks will be identified during the first year of this study. Soil abundance of this pathogen will be quantified and plants in these areas will be rated for disease severity on an ordinal scale of 1-5, where 1 means a completely healthy plant, and 5 means the plant is dead. We will return to these fields two times a year for the subsequent two years to sample soil and roots for quantification of M. phaseolina.
Objectives 2.1 and 2.2: Before fumigation we will collect infested crowns, leave them whole or cut them into half and quarter sizes, then bury them before fumigation. Soil gas concentrations of chloropicrin and 1,3-dichloropropene will be measured at the depths of 3”, 10”, and 20” for the duration that the tarp is on the field. After the re-entry interval, we will recover crowns from the field. In the lab, we will surface sterilize fragments in 1% sodium hypochlorite and plate them on selective media to test for the presence of the pathogen. For an untreated control we will assay 6 batches of 10 whole, half, and quarter crowns pre-treatment. During the subsequent strawberry season we will assess disease severity in each treatment with drone imagery to determine canopy establishment.
