Rootstock and Plastic Mulch Effect on Watermelon Flowering and Fruit Maturity in a Verticillium dahliae–Infested Field

Abstract

Separately, grafting and the use of plastic mulch can increase yield, quality, and early harvest of watermelon (Citrullus lanatus), especially when plants are under biotic and/or abiotic stress. A 2-year field study was conducted to evaluate the combination of four different rootstocks and two types of plastic mulch (black and clear) on date of watermelon first flowering, fruit ripening, yield, and fruit quality when plants were exposed to Verticillium dahliae. Seedless watermelon cv. Secretariat was grafted onto rootstocks Lagenaria siceraria cv. Pelop, Benincasa hispida cv. Round, and two interspecific hybrid squash rootstocks Cucurbita maxima × C. moschata cvs. Super Shintosa and Tetsukabuto, with nongrafted ‘Secretariat’ as the control. Fruit were harvested 0, 7, and 14 days after both the leaflet and tendril attached to the fruit pedicel were completely dry (fruit considered to be physiologically mature). The area under the disease progress curve (AUDPC) values for verticillium wilt were not different for mulch type in either year, although the overall AUDPC value was greatly reduced in the four grafted treatments (227) compared with nongrafted (743). There was no difference in days to male or female flowering due to mulch type or year, and rootstock did not affect first flowering of male flowers. Female flowering was 14 and 11 days later in 2018 and 2019, respectively, for ‘Secretariat’ grafted onto bottle gourd ‘Round’ compared with ‘Secretariat’ grafted onto ‘Tetsukabuto’. Female flowering of ‘Secretariat’ on ‘Round’ was also 7 days later compared with nongrafted ‘Secretariat’ both years. However, days to first harvest was not different with mulch or rootstock and was 92 days after transplanting (DAT) in 2018 and 114 DAT in 2019. There was no difference in yield (fruit number and weight) due to year, harvest date, or mulch, but there was a difference due to grafting. ‘Secretariat’ grafted onto ‘Super Shintosa’ had the greatest total number and weight of fruit per plant (3.7 and 14.8 kg, respectively), and nongrafted ‘Secretariat’ had the lowest (0.7 and 3.2 kg, respectively). Fruit quality attributes hollow heart formation (rating 3.2/5 on average), hard seed count (6 on average), total soluble solids (11% on average), and lycopene content were not different among mulch type, rootstock treatment, or harvest date; however, lycopene content did differ due to year (52.44 and 32.51 µg·g−1 in 2018 and 2019, respectively). Flesh firmness was highest for watermelon grafted onto ‘Super Shintosa’ rootstock (6.7 N) and lowest for nongrafted watermelon (4.3 N). Overall, rootstocks reduced verticillium wilt severity and increased fruit yield whereas mulch had no effects, and 5 V. dahliae colony forming units (cfu)/g of soil may be the minimum level for impact on watermelon fruit yield.

Inevitable Role of Grafting in Improvement of Cucurbitaceous Crops: A Review

“…"Crimson Sweet" watermelon grafted onto "Emphasis" and "Strongtoza" rootstocks grew more quickly and were more resistant to V. dahliae when compared to non-grafted plants (Buller et al, 2013). Devi et al (2020) found that Verticillium wilt severity differed between grafted watermelon plants and non-grafted 'Secretariat' watermelon plants. Grafted watermelon plants had 3.5 times less disease than non-grafted ones.…”

Progress in grafting watermelon to manage Verticillium wilt

“…Crimson Sweet was grafted onto rootstock cvs Mammoth, Calago, and Dako, compared to nongrafted (80%), when grown in soil artificially infested with an inoculum suspension of 10 6 conidia per ml. An additional study was conducted by Devi et al (2020) at Mount Vernon in the same field used by Attavar et al 2020 In five experiments over 4 years at Mount Vernon, WA, the AUDPC for watermelon grafted onto Tetsukabuto was always less than nongrafted plants, both grown with black plastic mulch ( Figure 4) (Attavar et al, 2020;Dabirian et al, 2017;Devi et al, 2020;Wimer et al, 2015b). When data from these four studies were analysed together, wilt generally was more severe on nongrafted Tri-X Palomar, the scion used in 2015, than on Sugar Baby or Secretariat, the scions used in 2014 or 2018-2019, respectively.…”

“…The average total fruit weight was 9.4 kg per plant. Devi et al (2020) Super Shintosa (C. maxima Dotted and dashed lines show 95% confidence intervals for the grafted and nongrafted watermelon regression lines, respectively. The slope of the regression line for nongrafted plants increases with increasing density (p = .03), but the slope for grafted plants does not increase significantly with increasing density (p = .08).…”

Effect of Grafting Compatibility on Fruit Yield and Quality of Cantaloupe in a Mediterranean-Type Climate

“…Studies on field production of grafted melons in a cool Mediterranean-type climate such as northwest Washington are limited to watermelon but not cantaloupe [34][35][36]. Rootstocks may have optimal soil temperature and moisture ranges and it is important to assess scion-rootstock combinations under the climatic and geographic conditions where the crop will be produced [31].…”