Screening tomato varieties for suitability on Guam in response to the arrival of Tomato leaf curl Guam virus in the Western Region

Screening tomato varieties for suitability on Guam in response to the arrival of Tomato leaf curl Guam virus in the Western Region

Summary

This report covers the period of April 1, 2014 through March 31, 2015. After collaboration with the plant virologist from the USDA-ARS U.S. Vegetable Laboratory, it was recommended that the virus be identified as Ageratum yellow vein virus (AYVV) rather than Tomato leaf curl Guam virus (TLCGV).

During the project’s first year, producers participated in a tomato leaf curl virus training and the wet-season variety trial. Data was gathered throughout the wet-season trial, which comprised of (1) germination rate and height, (2) virus severity in the field, (3) insect or disease damage on plants, (4) first flower and fruiting, (5) harvest/yield, and (6) producer selection of top varieties. Additionally, a virus severity scale was created to assist in the rating of tomato fields. Closing the project’s first year was the start of the dry-season variety trial, which began in February 27, 2015 and is still ongoing.

First year purchases included tomato variety seeds, a field scale, harvesting buckets, and germination supplies.

Objectives/Performance Targets

The first of the project’s three specific and measureable objectives was achieved during the first year, which was to improve the ability of producers to screen tomato varieties for Tomato leaf curl Guam virus (TLCGV) resistance and suitability for production on Guam.

This objective was fulfilled through several activities which include:

• Consultation with the project statistician.
• Training and education with the producers on virus identification and data collection.
• Scoring tomato varieties for resistance to TLCGV and suitability for production on Guam.
• During the training producers were given pre- and post-tests to measure knowledge gained.
• Producers reviewed the characteristics of 40 varieties prepared by the project graduate student and PI and selected the 17 varieties that were included in the trial along with the variety ‘Season Red’. Refer to Table 1 for a listing of varieties with corresponding field ID.
• Completion of the wet season variety screening trial from August 2014 to December 2014.
• A producer field day was held on December 14, 2014 where members re-evaluated plots and identified the top varieties from each field.
• On February 27, 2015 producers began the dry season variety trial.

The following are the remaining two objectives, which will be achieved during the second and third year of the project:

Objective 2: Bring awareness to producers and the public about Guam’s whitefly transmitted tomato virus and steps that can be followed to reduce its impact.

Objective 3: Bring about the adoption of farm practices that will reduce the occurrence of TLCGV in tomato fields and result in produce production returning to pre- Tomato leaf curl Guam virus levels.

• Table 1: List of varieties used for the varietal trial

Accomplishments/Milestones

Significant accomplishments of this project’s first year are the completion of the wet season varietal trial and the start of the dry season trial. During Guam’s wet-season beginning on August 2014, farm trials were begun to compare 17 commercial tomato varieties for virus resistance and production suitability against the control variety ‘Season Red’ (Table 1). Varieties selected consist of grape, cherry, elongate, globe, plum, roma, oval, or round tomato fruits that are either determinate or indeterminate. Harvest data was collected throughout the wet season varietal trial (Table 2). A tomato virus severity scale (Image 1) was created and used to visually evaluate the tomato varieties for Ageratum yellow vein virus (AYVV). Three times throughout the wet-season trial, fields were evaluated for AYVV; approximately one, two, and three months after transplant. Following the third virus severity evaluation, samples were collected from each field trial and pooled for Real-time PCR analysis at the USDA-ARS Vegetable Laboratory (Table 3). At the conclusion of the wet-season field trial, producers surveyed the participating farm trials and identified the top varieties in each field (Table 4). Additionally, brix analysis of each tomato variety was conducted and the end of the trial (Table 5).

Partial analysis of the third set of field data was conducted by the project statistician to identify virus resistance. Tomato varieties were compared against the control variety, ‘Season Red’, and analyzed using a cumulative logit model (Table 3). Virus severity was a natural ordinal response variable. Variety ID vs. Control was an explanatory where each variety was compared against the control variety. Plot ID was added into the model as a blocking factor to improve the model’s fit.

Early obstacles of this project included a change of two participants, poor weather conditions, and insect damage at the beginning of the field trial. Our original list of producers included John Mesa, Bernard Watson, Vicente Velasquez, Vincent Quichocho, and Edward San Nicolas. However, two of our participants, Vincent Quichocho and Edward San Nicolas, were no longer able to participate in this tomato study; therefore, Enrique Guerrero and Thahn Nguyen were substituted for them. Shortly after field transplanting, fields suffered rain, wind, and insect damage. As a result, those tomato seedlings that were dead were replaced.

Another obstacle that was overcome was the change in availability of producer Bernard Watson. He was able to participate solely in the wet-season variety trial and not the dry-season. Therefore, Bernard’s field was used to conduct a separate replicated trial during the wet-season. On October 2014, three replicated plots were set-up in Bernard Watson’s field, which was completed on January 9, 2015. Harvest data collected from the replicated trial can be found in Table 2. Pooled samples from each variety were sent to the USDA-ARS Vegetable Laboratory for Real-time PCR analysis. Although the plants in this replicated trial exhibited severe leaf curling, stunting, and yellowing, results from their analysis found all samples to be negative for AYVV with the exception of 1, which was ‘Tribute’ (field id # 18). The negative results for AYVV from the replicated trial could indicate a second virus with the same symptoms as AYVV.

• Table 4: Producer variety ranking
• Image 1: Tomato virus severity scale
• Table 1: List of varieties used for the varietal trial
• Table 2: Wet season varietal trial harvest data
• Table 3: Ranking of varieties, from resistant to susceptible, based on visual evaluation in comparison to Season Red, with corresponding Real-time PCR detection of AYVV
• Table 5: Brix analysis

Impacts and Contributions/Outcomes

The top varieties from each field were selected and ranked by producers and were ‘Olivia’, ‘Carmine’, ‘Affinity’, ‘Ornela’, and ‘Felicity’. These varieties were recommended for production on Guam based on their strong virus resistance, high yield, and low levels of cracked and unmarketable fruits.

The partial analysis of variety resistance identified 12 varieties with virus resistance superior to ‘Season Red’ and five with inferior resistance. Those varieties with superior resistance include: 3, 9, 12, 7, 1, 4, 5, 14, 11, 15, 10, and 17, while 16, 6, 18, 8, and 2 were identified as inferior to ‘Season Red’ (refer to Table 1 for the corresponding variety name for each field ID). Based on Real-time PCR of pooled samples, AYVV was detected in one superior variety and four of the inferior ones. When symptomless tomatoes were tested, only one of the 18 varieties were positive for AYVV.

Based on Real-time PCR of pooled samples, AYVV was detected in one superior variety and four of the inferior ones. When symptomless tomatoes were tested, only one of the 18 varieties were positive for AYVV. Image 2 illustrates the fruit types of the selected varieties, either grape, cherry, globe, or oval fruit. In a separate replicated trial planted on October 2014, plants again exhibited AYVV symptoms; however, Real-time PCR analysis showed low frequencies of the virus. This may indicate the presence of another virus affecting tomato production.

Results from the wet season varietal trail were presented in a poster at the 8^th International Symposium (Image 3) on March 2015.

• Image 2: Fruit types of varieties selected by producers, compared to Season Red
• Image 3: Tomato virus variety trial poster, results from the wet season variety trial
• Table 1: List of varieties used for the varietal trial

Collaborators: