Grafting Snake Melon [ Cucumis melo L. subsp. melo Var. flexuosus (L.) Naudin] in Organic Farming: Effects on Agronomic Performance; Resistance to Pathogens; Sugar, Acid, and VOC Profiles; and Consumer Acceptance

Abstract

The performance of snake melon [Cucumis melo var. flexuosus (L.)] in organic farming was studied under high biotic and salt stress conditions. Soilborne diseases (mainly caused by Macrophomina phaseolina and Neocosmospora falciformis), combined with virus incidence [Watermelon mosaic virus (WMV), Zucchini yellow mosaic virus (ZYMV), and Tomato leaf curl New Delhi virus (ToLCNDV)] and Podosphaera xanthii attacks, reduced yield by more than 50%. Snake melon susceptibility to M. phaseolina and Monosporascus cannonballus was proved in pathogenicity tests, while it showed some degree of resistance to Neocosmospora keratoplastica and N. falciformis. On the contrary, salt stress had a minor impact, although a synergic effect was detected: yield losses caused by biotic stress increased dramatically when combined with salt stress. Under biotic stress, grafting onto the melon F₁Pat81 and wild Cucumis rootstocks consistently reduced plant mortality in different agroecological conditions, with a better performance compared to classic Cucurbita commercial hybrids. Yield was even improved under saline conditions in grafted plants. A negative effect was detected, though, on consumer acceptability, especially with the use of Cucurbita rootstocks. Cucumis F₁Pat81 rootstock minimized this side effect, which was probably related to changes in the profile of sugars, acids, and volatiles. Grafting affected sugars and organic acid contents, with this effect being more accentuated with the use of Cucurbita rootstocks than with Cucumis. In fact, the latter had a higher impact on the volatile organic compound profile than on sugar and acid profile, which may have resulted in a lower effect on consumer perception. The use of Cucumis rootstocks seems to be a strategy to enable organic farming production of snake melon targeted to high-quality markets in order to promote the cultivation of this neglected crop.

Keywords: flexuosus; fruit quality; grafting; organic agriculture; soilborne pathogens.

FIGURE 1

Snake melon fruit in the field ready to be harvested (A) and harvested fruit (B). Characterization of snake melons (C,D).

FIGURE 2

(A) Average damage scores (from 0 to 4) of the stem lesions caused by M. phaseolina in snake melon and sweet melon control (Piel de Sapo Piñonet) at 7 and 15 days after inoculation (DAI). (B) Average damage scores (from 0 to 4) caused by M. cannonballus in primary and lateral roots of snake melon and sweet melon control at 30 DAI. Average area under the disease progress curve (AUDPC), average damage score, type of reaction (R, resistant; MR, moderately resistant), and disease incidence (%) for snake melon and the sweet melon control plants (Piel de Sapo Don Quixote) inoculated with N. falciformis (C) and N. keratoplastica (D). Six (A,B) and seven (C,D) biological replicates (plants) were used for each genotype.

FIGURE 3

Cumulative production (kg plant^–1) of non-grafted (NG) snake melons in 2018, cultivated in the three fields. Sixteen NG plants were cultivated per field. All fruits of marketable size were weighted at the time of harvest to estimate total yield per plant.

FIGURE 4

Cumulative production (kg plant^–1) of snake melons in 2018 grown in La Punta (A) and Carrizales (B) obtained from non-grafted plants and plants grafted onto the commercial Cucurbita hybrid Cobalt and the experimental C. melo hybrid F₁Pat81. Sixteen plants were cultivated per field and treatment. All fruits of marketable size were weighted at the time of harvest to estimate total yield per plant.

FIGURE 5

Cumulative production (kg plant^–1) of snake melons in 2019 from non-grafted plants and plants grafted on commercial Cucurbita hybrids (Cobalt and Shintoza), the C. melo hybrid F₁Pat81, and hybrids between C. ficifolius and C. anguria (Fian) or C. myriocarpus (Fimy) in the two sites of cultivation La Punta (A) and Carrizales (B). Sixteen plants were cultivated per field and treatment. All fruits of marketable size were weighted at the time of harvest to estimate total yield per plant.

FIGURE 6

Mean flavor acceptability (1 being the lowest and 5 being the highest) obtained in the sensory evaluations of 2018. Columns of lighter color indicate that the fruit samples were from La Punta and those of darker color indicate that they are from Carrizales. Values followed by (*) show significant differences compared to the NG control (Dunnett’s test, P ≤ 0.05). Averages are calculated with the mean scores of 20 panelists on three biological replicates (fruit samples) of each treatment.

FIGURE 7

Mean texture, aroma, and flavor acceptability scores (1 being the lowest and 5 being the highest) obtained in the sensory evaluations of 2019. Columns of lighter color indicate that the fruit samples were obtained from La Punta and those of darker color indicate that they were obtained from Carrizales. Columns with (*) show significant differences compared to the NG control (Dunnett’s test, P ≤ 0.05). Averages are calculated with the mean scores of 20 panelists on three biological replicates (fruit samples) of each treatment. (A,C,E) Correspond to sensory evaluations 1 and 5. (B,D,F) Correspond to sensory evaluations 2, 3, and 4.

FIGURE 8

Accumulation of sugars and acids in fruits from non-grafted and grafted (Shintoza, F1Pat81, and Fian) snake melon plants from Carrizales (A) and La Punta (B). Columns with (^∗) show significant differences with respect to the NG control (Dunnett’s test, P ≤ 0.05). Averages were calculated from the biological replicates used in the sensory evaluations. From those treatments included in the five sensory evaluations of 2019, NG and F₁Pat81, averages were calculated from six and four biological replicates, respectively, from the three sensory evaluations of la Punta and the two sensory evaluations of Carrizales. Four and three biological replicates were averaged, respectively, for the Shintoza treatment, included in two sensory evaluations from La Punta and one sensory evaluation from Carrizales. Two biological replicates were averaged for the Fian treatment from each of the two sensory evaluations in which this treatment was included (one from La Punta and one from Carrizales).

FIGURE 9

Accumulation of volatile organic compounds in fruits from non-grafted and grafted (Shintoza, F₁Pat81, and Fian) snake melon plants from Carrizales (A) and La Punta (B). Samples obtained from the sensory analyses performed in 2019. Columns with (^∗) show significant differences with respect to the NG control (Dunnett’s test, P ≤ 0.05). Averages were calculated from the biological replicates used in the sensory evaluations as described in legend of Figure 8.

FIGURE 10

Biplots of scores (bold) and loadings (italics) obtained in the principal component analyses performed with the contents of volatile organic compounds in fruits from non-grafted (NG) and grafted (Shintoza, F₁Pat81, and Fian) grown at La Punta (A) and Carrizales (B). Samples obtained from the sensory analyses performed in 2019 as described in legend of Figure 8. 1_1, 1-pentanol; 1_2, (Z)-3-hexen-1-ol; 1_3, 1-nonanol; 1_4, (Z)-3-nonen-1-ol; 1_5, benzyl alcohol; 1_6, phenol; 1_7, phenylethanol; 1_8, 1-hexanol; 2_1, hexanal; 2_2, heptanal; 2_3, (E)-2-heptenal; 2_4, (E,E)-2,4-heptadienal; 2_5, (E)-2-octenal; 2_6, nonanal; 2_7, (Z)-6-nonenal; 2_8, (E)-2-nonenal; 2_9, (E,E)-2,4-nonadienal; 2_10, (E,Z)-2,6-nonadienal; 2_11, (E,E)-2,4-decadienal; 2_12, benzaldehyde; 2_13, phenylacetaldehyde; 3_1, 2-methyl propyl acetate; 3_2, (E,E)-2,4-headienoic acid, ethyl ester; 3_3, butyl butyrate; 3_4, ethyl butanoate; 4_1, 6-methyl-5-hepten-2-one; 4_2, geranylacetone; 4_3, beta-ionone; 4_4, beta-cyclocitral.

FIGURE 11

Heatmap of correlation analyses performed with data from the sensory evaluation and metabolite contents of the samples of 2019. 1_1, 1-pentanol; 1_2, (Z)-3-hexen-1-ol; 1_3, 1-nonanol; 1_4, (Z)-3-nonen-1-ol; 1_5, benzyl alcohol; 1_6, phenol; 1_7, 2-phenylethanol; 1_8, 1-hexanol; 2_1, hexanal; 2_2, heptanal; 2_3, (E)-2-heptenal; 2_4, (E,E)-2,4-heptadienal; 2_5, (E)-2-octenal; 2_6, nonanal; 2_7, (Z)-6-nonenal; 2_8, (E)-2-nonenal; 2_9, (E,E)-2,4-nonadienal; 2_10, (E,Z)-2,6-nonadienal; 2_11, (E,E)-2,4-decadienal; 2_12, benzaldehyde; 2_13, phenylacetaldehyde; 3_1, 2-methyl propyl acetate; 3_2, (E,E)-2,4-hexadienoic acid, ethyl ester; 3_3, butyl butyrate; 3_4, ethyl butanoate; 4_1, 6-methyl-5-hepten-2-one; 4_2, geranylacetone; 4_3, beta-ionone; 4_4, beta-cyclocitral.