Date of Award

Fall 2017

Project Type

Thesis

Program or Major

Plant Biology

Degree Name

Master of Science

First Advisor

J. Brent Loy

Second Advisor

Rebecca Grube Sideman

Third Advisor

Cheryl Smith

Abstract

Melons [Cucumis melo L.], are potentially a high value crop for New England, but production is limited by cool soil temperatures and sudden wilt. The primary symptom of sudden wilt syndrome is rapid wilting of vines either just preceding or during the harvest period when plants have a heavy fruit-load. Typically, plants do not recover from these symptoms, resulting in reduced yield and fruit quality. The exact cause of sudden wilt is unknown; however, the main cause is thought to be a soil-borne pathogen with other compounding abiotic factors. Use of early cultivars, black plastic mulch, and rowcovers have brought about earlier melon yields, but has not reduced the occurrence of sudden wilt. Melons grafted to rootstocks of interspecific hybrid squash [Cucurbita maxima Duchesne x Cucurbita moschata Duchesne] have exhibited increased tolerance to soil-borne diseases, along with tolerance to cold soils for early season transplantation. In a 2015 study, the performance of ‘Halona’ melon grafted to four different rootstocks was evaluated in two separate plots at Kingman and Woodman Research Farms, in Madbury and Durham, NH, respectively. In 2016, two additional studies were performed at the Kingman Research Farm to compare grafted and non-grafted melons for season extension, and to evaluate the rootstock for use with five popular New England cultivars. For the season extension study, and using NH1320 rootstock, the performance of grafted and non-grafted ‘Halona’ melon plants were compared at three transplantation dates, two early (12 May and 21 May) and a standard schedule (1 June), and two irrigation frequencies. Plants were grown on raised beds mulched with black plastic and irrigated with drip tape. Wide floating rowcovers were used as necessary during cool periods. For the cultivar-grafting study, the yield and quality of the following melon cultivars were evaluated: ‘Sarah’s Choice’, ‘Athena’, ‘Diplomat’, ‘Goddess’, and ‘Snow Leopard’, grafted to ‘Carnivor’ rootstock.

In 2015, two of the four rootstocks did not perform well, and NH1320 and Carnivor rootstocks were chosen for follow-up studies in 2016. Non-grafted plants generally exceeded that of grafted plants in early growth, and flowered generally five to eight days prior to grafted plants. However, by the first harvest period, vegetative growth of grafted plants was appreciably greater than that of non-grafted plants. Non-grafted plants, despite the earlier melon yields compared to grafted plants, had succumbed to sudden wilt by mid-August, which compromised additional yields. In contrast, grafted melons maintained growth and continued to set fruit over a longer time-period, thus affording a longer market window. Harvests of grafted ‘Halona’ melon were three to eight days earlier with non-grafted as compared to grafted plants at all three planting dates, but total marketable yields of grafted plants compared to non-grafted plants were 131%, 123% and 148% higher by planting dates on May 12, May 21, and June 1, respectively. Yield increases were due to both fruit number and fruit size in grafted compared to non-grafted melons from all three planting dates. SSC was not significantly different between grafted (10.7-11.4%) and non-grafted (10.7-11.8%) across all three planting dates. Fruit yields of grafted plants extrapolated to 98.6, 87.1 and 95.5 t·ha-1, respectively, in plots at the May 12, May 21, and June 1 planting dates. Similar increases in yield of grafted as compared to non-grafted plants were exhibited in the five cultivars grafted to the Carnivor rootstock, but the magnitude of increase varied among cultivars. Total marketable yields of grafted plants were 36% to 90% higher than that of non-grafted plants. Differences in fruit developmental patterns occurred among cultivars in both grafted and non-grafted plants. Grafted plants of ‘Sarah’s Choice’ and ‘Athena’ exhibited both later maturity and large differences in peak production compared to non-grafted plants. Grafted ‘Diplomat’, ‘Goddess’, and ‘Snow Leopard’ exhibited less differences in first harvest and a larger window of productivity than non-grafted plants. Depending on the cultivar, average fruit size was significantly larger in grafted plants (2.02-3.1 kg) as compared to non-grafted plants (1.35 – 2.01 kg), with exception for ‘Snow Leopard’ which had similar fruit size of both grafted and non-grafted melons (1.2 kg). Mean SSCs were not significantly different between grafted and non-grafted cultivars with exception for ‘Diplomat’ which had higher SSCs in grafted melons. For all experiments, grafted plants exhibited more vigorous and sustained vegetative growth than non-grafted plants, increased FW yields between 36% and 147% and fruit SSCs were similar in grafted and non-grafted plants. Certainly, grafted melon plants have potential benefits for growers in New England who have experienced low yields due to sudden wilt, or are not able to justify the field space to such a short season crop. These results demonstrate the potential of grafting to reduce the effects of sudden wilt in melon, increase yields dramatically, and maintain fruit quality.

Download

Share

COinS