Assessing Root Characteristics of Cucurbit Rootstocks using a Simple Germination Test

Vegetable grafting has many benefits including disease resistance, stress tolerance, and vigorous growth. The most commonly used rootstocks in melon (Cucumis melo) production are interspecific hybrid squash rootstocks, which have Fusarium wilt resistance and vigorous root systems. Different rootstocks may vary greatly in their influence on growth vigor of grafted melon plants. In this study, a simple germination test was conducted to compare the initial growth of the root system among the different rootstocks that may be used for grafted melon production. ‘Athena’ muskmelon was used as the scion control, and seven commercial cucurbit rootstocks were evaluated, including ‘Strong Tosa’, ‘Shintosa Camel’, ‘Carnivor’, ‘Kazako’, ‘No.1’, ‘53009’, and ‘Dinero’. Seeds were germinated in an incubator at 27 °C for three days, until their emergence. Root growth was assessed daily between germination and full emergence of the cotyledons. Total root length, total root surface area, total root volume, and average root diameter were determined using a root scanner. However, at day 1, only root length was measured, since the root systems were too small for root scanner measurements. At day 1, ‘Athena’ scion and ‘No.1’ rootstock had significantly greater root length than the other rootstocks. Most rootstocks tested did not demonstrate more rapid increase in total root length compared to the ‘Athena’ scion; however, ‘No.1’ at day 2 and ‘No.1’ and ‘Carnivor’ at day 3 had greater root length than ‘Athena’. In contrast, ‘Shintosa Camel’ showed consistently the smallest root length during the germination test. For total root surface area, at day 2, ‘No.1’ and ‘Carnivor’ had significantly higher values than ‘Athena’ and by day 3, ‘53009’ also had significantly higher root surface area than ‘Athena’. Except for ‘Dinero’ and ‘Shintosa Camel’, five out of the seven rootstocks evaluated showed significantly higher root volume than ‘Athena’. ‘Dinero’ showed similar average root diameters as ‘Athena’ at day 2 and day 3, whereas all other rootstocks demonstrated larger root diameters than ‘Athena’. Overall, the ‘No.1’ rootstock showed the most vigorous root system in this germination test. Although this study will not reflect the growth and yield performance of grafted ‘Athena’ in field production, assessing root characteristics using germinated seeds may be a promising tool in the future for initial screening of rootstocks with vigorous root systems.