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Kristine M. Lang and Ajay Nair

High tunnels allow vegetable growers to extend the growing season, increase crop production, and improve produce quality. Tomatoes (Solanum lycopersicum L.) are the most widely grown crops in high tunnels; however, tomato production in high tunnels can be challenging. Continuous cropping in high tunnels can increase soil-borne disease pressure and can lead to soil salinity or nutrient depletion issues. Based on preliminary research, we hypothesized that use of the rootstock ‘RST-04-106-T’ would increase yield and quality of heirloom and hybrid tomato scions compared with nongrafted plants. To test this hypothesis, our research objectives were to assess marketable yields, fruit quality and nutritional value, and plant growth of grafted and nongrafted hybrid and heirloom tomatoes in a high tunnel production system. Grafted and nongrafted ‘Cherokee Purple’ (heirloom) and ‘Mountain Fresh Plus’ (hybrid) tomatoes were grown in the same high tunnel for two seasons (7 May–20 Oct. 2015 and 29 April–7 Oct. 2016) at the Horticulture Research Station in Ames, IA. Grafted plants produced significantly more marketable fruit, although marketable and total fruit weight did not increase significantly. Individual fruit size was unaffected by grafting. Across cultivars, mean soluble solids content (SSC) in fruit was 0.3 °Brix lower in grafted plants as compared with the nongrafted control. Grafting did not affect lycopene content of fruit. Grafting increased stem diameter by an average of 0.8 mm, but overall plant biomass was unaffected. The effect of grafting on leaf chlorophyll concentration (SPAD readings) was mixed. In addition, grafting increased leaf chlorophyll concentration in ‘Cherokee Purple’ but decreased it in ‘Mountain Fresh Plus’ plants. Grafting is a valuable tool in tomato production, but the impact of ‘RST-04-106-T’ rootstock use appears to be specific to certain soil types with high incidence of bacterial wilt.

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Kristine M. Lang, Ajay Nair and Kenneth J. Moore

Prior work in a Midwestern United States high tunnel indicated that hybrid and heirloom tomato scions grafted to hybrid rootstock ‘RST-04-106-T’ had a minimal yield increase in the absence of soilborne disease pressure, which underscored the need for continued regional trials of alternative, commercially available tomato rootstocks. Objectives of the present study were to assess yield, fruit quality [pH, soluble solids content (SSC), total titratable acids (TTA), and firmness], and plant growth traits (plant height, stem diameter, and biomass) of grafted tomato with eight different hybrid rootstocks. ‘BHN 589’, a determinate hybrid tomato, was grafted to ‘Arnold’, ‘Beaufort’, ‘DRO141TX’, ‘Estamino’, ‘Maxifort’, ‘RST-04-106-T’, and two trial rootstocks, ‘946 TRS’ and ‘980 TRS’. Research was conducted April to September in 2017 and 2018 in a 9.1-m wide × 29.2-m long × 3.7-m tall single-poly high tunnel located at the Iowa State University Horticulture Research Station, Ames, IA. There were five plants per treatment in a randomized complete block design with five replications. Weekly harvests took place 13 times each season. ‘BHN 589’ grafted to ‘Arnold’, ‘Beaufort’, ‘DRO141TX’, ‘Estamino’, or ‘Maxifort’ had 30% to 119% more marketable fruit and had a higher marketable fruit weight by 1.3 to 4.1 kg per plant compared with nongrafted plants. Fruit quality differences were minimal in 2017 and null in 2018, as indicated by fruit pH, SSC, TTA, and the SSC:TTA ratio. The same five high-yielding rootstock treatments were the tallest, ranging from 184 to 214 cm in height. In 2017, shoot biomass of ‘BHN 589’ grafted to ‘Arnold’, ‘Beaufort’, ‘DRO141TX’, ‘Estamino’, and ‘Maxifort’ was 59 to 100 g more than that of nongrafted plants; in 2018, ‘BHN 589’ grafted to ‘Maxifort’ and ‘DRO141TX’ had the largest shoot biomass at 386 and 315 g, respectively. Overall, the results of this study indicate that ‘Arnold’, ‘DRO141TX’, and ‘Estamino’ may be comparable in performance to the widely used rootstocks ‘Beaufort’ and ‘Maxifort’ when grown under conditions lacking biotic or abiotic stress. Our results provide promising new options for Midwestern U.S. growers of high tunnel tomato who are seeking high-performing rootstocks.

Open access

Kristine M. Lang, Ajay Nair and Kenneth J. Moore

Growing colored bell peppers in high tunnels enhances fruit quality and accelerates ripening. While there are benefits to high tunnel pepper production, increased heat inside the structures can lead to plant stress, blossom drop, sunscald, and reduced marketable yields. The objective of this study was to test shadecloth treatments placed on high tunnels to mitigate heat stress and improve colored bell pepper yield and fruit quality, while also identifying cultivars that perform well within Midwest high tunnel systems. Research was conducted at the Iowa State University Horticulture Research Station (Ames, IA) from 11 May to 11 Oct. in 2017 and 3 May to 9 Oct. in 2018. Six single-poly passively ventilated Quonset high tunnels were used for the experiment. The shade treatments (no shadecloth, 30% light-reducing shadecloth, and 50% light-reducing shadecloth) were applied in June of each season. Within each shade treatment, there were three randomized complete blocks of the seven colored bell pepper cultivars (Archimedes, Delirio, Flavorburst, Red Knight, Sirius, Summer Sweet, and Tequila). Data were collected on yield, fruit quality, and plant growth characteristics. Environmental parameters were monitored throughout the growing season. Both the 30% and 50% shadecloth treatments reduced monthly average and maximum air temperatures within high tunnels, with the largest differences occurring in the months of July and August. The use of a shadecloth reduced the incidence of sunscald by 59% between no shade and 50% shadecloth treatments. While there was no difference between 30% and 50% shade treatments, the use of 50% shadecloth caused a decrease in both marketable number (32%) and weight (29%) of pepper fruit compared with the control. ‘Tequila’, ‘Delirio’, and ‘Flavorburst’ had more marketable fruit per plant. Shade treatments did not affect fruit soluble solids content (SSC), pH, or total titratable acidity (TTA). Shade treatments had no effect on Soil Plant Analysis Development (SPAD) readings, shoot biomass, the number of leaves per plant or the total leaf area per plant; however, plant height increased by an average 14.5 cm for plants under shadecloth treatments. Average leaf size was 11.2 cm2 larger on plants grown under the 50% shadecloth, compared with the control. Several cultivar differences existed for each fruit quality and plant growth parameter. While differences in fruit quality and plant growth parameters were limited among shade treatments, decreasing marketable yield is concerning. Our research suggests that Midwest growers should not exceed 30% light-reducing shadecloth on their high tunnels for colored bell pepper production.