Davison, J., and Lattin, R. 2015, Evaluation of Several Tomato Varieties’ Resistance to Beet Curly Top Virus Grown Under High Tunnels and in the Field, University of Nevada Cooperative Extension

Summary:

During 2012 and 2013, seven tomato varieties were grown inside and outside of a Utah State University-type hoop house in Fallon, Nev. The tomatoes selected represented three types popular with local growers, Beefsteak, Roma and an Heirloom. The purpose of the project was to test two hypotheses: 1) Incidence of Beet Curly Top Virus (BCTV) is reduced in organic fresh market tomatoes grown under high tunnels, and 2) The use of locally developed BCTV-resistant plants reduces the incidence of BCTV in high-tunnel and field-grown organic fresh market tomatoes. The plants in the tomato trial were evaluated for yield (number and weight of fruits produced), appearance, percent marketable yield (2012) and plant survival (2013). This data was collected over three harvest periods in both years. The results indicated that plants grown in hoop houses produce higher yields with better quality fruit due to less damage from BCTV. The commercial varieties produced more and better fruit than the locally developed tomato varieties.

Introduction:

Small vegetable production in high tunnels or hoop houses is gaining in popularity throughout western Nevada. The increased interest is due to the desire of many people and businesses to purchase fresh, locally grown vegetables. Because western Nevada is subject to early and late plant-killing freezes, season-extending technologies such as hoop houses are an important production aid. The number of hoop houses used in small-scale production has grown exponentially, in part because federal financial assistance provided by the Natural Resources Conservation Service has greatly reduced the out-of-pocket expense to local growers. This, combined with the simplicity and low cost of the popular Utah State University hoop house design, has resulted in rapid growth in the number of hoop houses used. For example, in the Lahontan Valley of western Nevada there are approximately 84 hoop houses, whereas five years ago there were just a few.

Tomatoes are one of the most popular crops produced by the small growers of western Nevada. They are grown in the field and in hoop houses. Unfortunately, in many years the presence of Beet Curly Top Virus (BCTV) in the tomato plants severely reduces plant survival and subsequent fruit production. (1) Because of the difficulties in controlling the insect disease vector (leafhoppers) and the desire of many of the growers to produce organically, another method of reducing disease incidence without using chemicals is needed. Generally, management of this disease is recommended utilizing Integrated Pest Management (IPM) techniques. These include planting resistant varieties, providing shade to the tomato plants, utilizing row covers and increasing plant densities. (5) Production of tomatoes in hoop houses may be another technique to reduce the incidence of this important disease. (2) Hoop houses provide shade, higher humidity levels and dense planting patterns, all of which may contribute to lowered disease incidence. (3) In addition, a local plant breeder and tomato grower was reported to have developed tomato varieties which displayed resistance to BCTV. However, that claim had never been tested in a formal trial.

The local alternative crop specialist for University of Nevada Cooperative Extension worked with two western Nevada vegetable producers to test the following hypotheses: 1) Incidence of Beet Curly Top Virus (BCTV) is reduced in organic fresh market tomatoes grown under high tunnels, and 2) Use of locally developed BCTV-resistant plants reduces the incidence of BCTV in high-tunnel and field-grown organic fresh market tomatoes.

Experimental Methodology:

During 2012 and 2013 three tomato varieties available on the commercial market and three locally developed BCTV-resistant, tomato varieties were grown in a Utah State University-type high tunnel (hoop house) and an adjacent field (Table 1). The tomatoes selected represented three types popular with local growers, beefsteak, Roma and an heirloom. A different commercial beefsteak variety was substituted in 2013, as the 2012 variety was not available. The experiment was located on Fernley sands as described by the Natural Resources Conservation Service’s Fallon-Fernley soils survey. (4) The high tunnel measured 14 feet wide and 140 feet long. The tomato field trial was situated immediately adjacent to and south of the hoop-house planting.

The trial was planted in a randomized complete block design with three replications per block. The six treatments consisted of four tomato plants per replication, for a total of 144 plants sampled each year. The tomatoes were planted on June 5, 2012 and June 6, 2013 as transplants, averaging approximately 3 to 4 inches tall. The plants were drip-irrigated so that water was not a limiting factor. No chemical fertilizer or pest control materials were applied to the plants during the trial. Data collected included the number and weight of fruit produced per plot, an appearance rating (1 to 10, 10 = perfect appearance) of the fruits harvested from each plot, and the percent marketable fruits for each harvest. During 2013, the number of living plants was also recorded, as disease incidence was very high compared to 2012, when little to no disease symptoms was present on the plants. In 2013, leaf samples were obtained from all plants and sent to the Nevada Department of Agriculture pathology lab to test for the presence of BCTV. Three separate harvests of the plots were completed each year. The 2012 harvest occurred Aug. 14, Sept. 28 and Oct. 19. The 2013 harvests occurred on Sept. 3, Sept. 19 and Oct. 15. The final harvest of 2013 was only possible from the plants growing in the hoop house, as the field grown plants had all perished from killing frosts, which occurred Oct. 4, 5 and 6, 2013.

The data was analyzed using a paired t-test statistical package provided in the latest IBM Statistical Package for the Social Sciences (SPSS) program. Mean separation was determined at the P< 0.10 level of significance, meaning that any difference measured had a 90 percent chance of occurring due to the variety or planting location.

Table 1. Characteristics of tomato varieties planted in 2012 and 2013

*table here

Results:

During the 2012 production season, almost no BCTV occurred on any of the plants being evaluated or in adjacent production fields. Therefore no valid comparisons regarding the impact of BCTV on the selected varieties or production technique (high tunnel versus field) could be made. During 2013, the disease level appeared to be very high, and signs of the disease were evident in the field and hoop house plants. The disease signs included leathery, yellow, curled leaves with purple-colored veins. As the disease progressed, the entire plant turned brown and died. However, the viral testing protocol completed by the Nevada State Plant Pathologist reported no evidence of BCTV in any sample submitted (>300 samples). We have no explanation for this anomaly, as the disease signs were obviously evident, production was severely impacted on infected plants, and several plants died before any production occurred.

2012 Growing Season Results:

The first analysis in 2012 examined paired production for each variety, comparing plants grown in a hoop house with those produced in a field system. The analysis included the average yield in pounds, fruit numbers per plot, an appearance rating and marketability percent by the same tomato variety for plants produced inside and outside a hoop house. Table 2 depicts the results of these comparisons.

Table 2. Yield and quality differences between six tomato varieties grown in a hoop house and under field conditions during 2012.

*table here

The second analysis in 2012 evaluated the three commercial varieties with the three local varieties when grown in the field. The evaluations included yields, numbers, appearance ratings and the percent marketable. Table 3 presents the results of these evaluations

Table 3. Yield and quality differences between three commercial and three local tomato varieties grown under field conditions.

*table here

The third evaluation examined the same factors as the previous one, but the comparison was conducted among plants produced in a hoop house. Table 4 is composed of these results.

Table 4. Yield and quality differences between three commercial and three local tomato varieties grown in a hoop house.

*table here

The last factor examined in 2012 was the percentage of production by harvest. This was completed to determine if the plants grown in the hoop house produced fruits earlier than those grown under field conditions, and if production was different at the end of the season when temperatures were much cooler. This would be important in Nevada, as tomatoes produced early in the season typically sell for more than those produced later, and early frosts can severely reduce production later in the season. Therefore while total yields may be similar, total income may be higher from hoop-house tomatoes planted at the same time as field-grown plants. Figure 1 is a graphic representation of the results resulting from these trials in 2012.

Figure 1. Distribution of tomato production over three harvests from plants grown in the field and in a hoop house during 2012. (Average production in pounds/ plot.)

2013 Growing Season Results:

The 2013 growing season was much different than the 2012 growing season in two ways. The observed disease incidence was much higher in 2013 than 2012. The higher disease incidence resulted in a larger percentage of individual plant deaths and a subsequent reduction in yields. The other difference was a series of frosts that occurred in early October and killed all the tomato plants growing outside the hoop house. 

As in the previous year, the plants were harvested by hand by experienced pickers who counted, weighed and rated the tomato fruits at each harvest. The data gathered included the number of fruits per plot, the average yields in pounds, an appearance rating and the number of live plants per plot, with four plants being possible.

The first analysis in 2013 examined paired production for each variety, comparing plants grown in a hoop house with those produced in a field system. The analysis included mean yield in pounds, fruit numbers per plot, an appearance rating and marketability percent by variety for plants produced inside and outside a hoop house. The purpose of this analysis was to compare production characteristics of the same varieties grown inside and outside. Table 5 depicts the results of these comparisons.

Hoop house production (right) Field system production (left)

hoop house productionfield system production

Table 5. Yield and quality differences between six tomato varieties grown in a hoop house and under field conditions during 2013.

*table here

The second analysis in 2013 evaluated the three commercial varieties with the three local varieties when grown in the field. The evaluations included yields, numbers, appearance ratings and the number of live plants per plot. Table 6 presents the results of these evaluations.

Table 6. Yield and quality differences between three commercial and three local tomato varieties grown under field conditions in 2013.

*table here

The third evaluation in 2013 examined the same factors as the previous one, but the comparison was conducted among plants produced in a hoop house. Table 7 is composed of these results.

Table 7. Yield and quality differences between three commercial and three local tomato varieties grown in a hoop house in 2013.

*table here

The last factor examined in 2013 was the percentage of production by harvest. This was completed to determine if the plants grown in the hoop house produced fruits earlier than those grown under field conditions, and if production was different at the end of the season when temperatures were much cooler. 

This would be important in Nevada, as tomatoes produced early in the season typically sell for more than those produced later, and early frosts can severely reduce production later in the season. Therefore while total yields may be similar, total income may be higher from hoop-house tomatoes planted at the same time as field-grown plants. Figure 2 is a graphic representation of the results resulting from these trials in 2013.

Figure 2. Distribution of tomato production over three harvests from plants grown in the field and in a hoop house during 2013. (Average production in pounds/plot).

*table here

Discussion:

Although relatively few of the measured variables indicated statistically significant differences during 2012 when disease pressures were very light, a strong trend toward increased production by plants grown in the hoop house is obvious. All tested varieties grown in a hoop house produced higher yields and earlier fruit than those grown under field conditions. There were fewer and more variable differences regarding the appearance of the fruit and marketable percentages in the hoop-house tomatoes. In some of these cases the field-grown plants produced a larger number of fruits (Roma, Korena’s Roma and big beef), with higher average appearance ratings (Cherokee) and larger marketing percentages. The three commercial varieties surpassed the three local varieties in every category measured when grown under field conditions. The differences were much less pronounced when all of these plants were grown in the hoop house, and in one instance, the local variety “Mewaldt’s Cherokee” produced a slightly higher percentage of marketable fruit as compared to the commercial Cherokee variety.

The 2013 production season was very different, in that signs and symptoms of disease damage were much more apparent on plants grown inside and in the field. Although viral testing did not indicate the presence of BCTV, the appearance and high mortality of affected plants indicated a severe disease incidence. Visual appraisals by numerous experienced producers determined that plants growing adjacent to the edge of the hoop house where the sides were rolled up, exposing the plants to outside conditions, displayed a higher incidence of disease damage when compared to those growing in the center of the hoop house. Nearly all the field-grown plants displayed varying signs of disease, with mortality approximately two times that of the plants growing in the hoop house. Yields were significantly higher for all tomato varieties of plants grown in the hoop house as compared to those grown under field conditions. This was partly due to the fact that the number of surviving plants per treatment was also significantly higher in every instance in the hoop-house grown plants. A second factor resulting in the higher production related to the hoop-house grown plants was a killing freeze that occurred prior to the last harvest of the season. The plants growing in the hoop house were unaffected, while no tomatoes were harvested from those growing outside after the early October frost. No differences were detected between the hoop-house and field-grown plants in regards to the average number of fruits per plant or the appearance ratings.

When the commercial varieties were compared to the locally developed tomato varieties grown in the hoop house or in the field, only minor differences were detected. Under field-grown conditions the commercial variety Roma VF produced significantly greater yields than the locally developed Korena’s Roma. In the hoop house the number of fruit per plant was significantly higher in Korena’s Roma, which is a locally developed variety, as opposed to the commercial Roma VF. No other differences were noted. All hoop-house grown tomatoes produced fruits earlier than those grown in the field. As previously noted, early production is typically worth more money than later harvests, which conveys an additional advantage to the plants growing in the hoop house.

The results obtained over the past two production seasons verify the advantages to growing tomatoes in hoop houses as compared to growing them in a field situation. Under light disease pressure, production from the hoop-house plants was higher and fruit was available earlier. Under heavy disease pressure, production was higher and again available earlier in the season from the plants growing in a hoop house. Hoop-house tomatoes displayed another advantage when an early frost in 2013 prevented a third harvest of the plants growing in the field, while production from the plants growing in a hoop house was unaffected. When all the advantages are considered, hoop-house production of tomatoes in western Nevada can be recommended as a viable practice, especially for small-acreage growers.

References:

(1) Damicone, J., and L. Brandenberger. 2014 Common Diseases of Tomatoes-Part II, Diseases caused by Bacteria, Viruses and Nematodes. Oklahoma Cooperative Extension Service. Fact sheet EPP-7626. Oklahoma State University, Stillwater, Oklahoma. pp-4,5. Common Diseases of Tomatoes - Part II Diseases Caused by Bacteria, Viruses, and Nematodes Accessed December 22, 2014.

(2) Gatzke, H. 2012. Hoop house production in the desert; Solanaceae and Cucurbitaceae crops. University of Nevada Cooperative Extension, Special Publication 12-07. University of Nevada Reno, Reno, Nevada. 12 pp.

(3) Hefflebower, R., Reid, C., Frank, E., and K. Evens. 2008. Curly Top of Tomatoes. Utah Pests Fact Sheet, PLP-007. Utah State University Extension. Logan, Utah. 3pp.

(4) Soil Survey Staff. 2014 Natural Resources Conservation Service, United States Department of Agriculture. Web Soil Survey. Available online at Web Soil Survey Accessed December 22, 2014.

(5) UC Pest Management Guidelines, 2013. Tomato, Curly Top. Agriculture and Natural Resources, University of California. Available online at Tomato, Curly Top Accessed December 22 2014.

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