3.2 Response of Luffa spp. accessions to M. pseudophaseolina inoculation
Data from both experiments were combined since no significant effect of the experiment repetitions was observed (ANOVA p > 0.05) for all the variables analyzed. Inoculation of cucurbits by M. pseudophaseolina revealed statistically significant differences for disease incidence and severity, as demonstrated by the Kruskal-Wallis test at a 5% probability (p ≤ 0.05) (Table 3), and for SL, RL, FSW, FRW, DSW, and DRW, as indicated by the Scott-Knott test at a 5% probability (p ≤ 0.05) (Table 4).
Table 3
Disease incidence and severity, and reaction class against Macrophomina pseudophaseolina inoculation in accessions of Luffa spp., Cucumis melo, and Citrullus lanatus.
Treatment/ accessions | Disease incidence | Disease severity | Reactionc |
Ranka | Mean (%) | Ranka | Meanb |
AB07 | 67.5 b | 100.0 | 45.1 a-d | 2.1 | SU |
AB24 | 46.5 ab | 63.0 | 37.1 a-c | 1.7 | MR |
AB26 | 67.5 b | 100.0 | 60.2 a-d | 3.1 | SU |
AB36 | 67.5 b | 100.0 | 60.2 a-d | 3.1 | SU |
AB39 | 11.5 a | 0.0 | 11.5 a | 0.0 | I |
AB40 | 67.5 b | 100.0 | 85.4 cd | 4.5 | HS |
AB41 | 67.5 b | 100.0 | 93.0 d | 5.0 | HS |
AB44 | 67.5 b | 100.0 | 85.0 cd | 4.6 | HS |
AB50 | 67.5 b | 100.0 | 93.0 d | 5.0 | HS |
AB51 | 39.5 ab | 50.0 | 32.5 a-c | 1.5 | MR |
AB52 | 67.5 b | 100.0 | 65.0 a-d | 3.5 | SU |
AB55 | 53.5 b | 75.0 | 27.2 ab | 0.8 | HR |
Melon | 67.5 b | 100.0 | 75.4 b-d | 4.1 | HS |
Watermelon | 32.5 ab | 38.0 | 21.1 ab | 0.5 | HR |
χ 2 | 65.5 | | 80.3 | | |
χ 2 = significant chi-squared values at 5% probability. a Values followed by the same letter within columns do not differ statistically from each other by the Kruskal-Wallis non-parametric test (p ≤ 0.05). b Average scores for all observations within each sample following the diagrammatic scale: 0 (no symptoms) and 5 (more than 50% of infected tissues) (Ravf & Ahmad, 1998). c Reaction to the disease according to Salari et al. (2012), wherein: I = immune; HR = highly resistant; MR = moderately resistant; SU = susceptible; and HS = highly susceptible. Data are average values from two experiments, each with four replicates (pots) per treatment and one plant per pot.
Table 4
Averages of lengths and fresh and dry weights of shoots and roots in accessions of Luffa spp., Cucumis melo, and Citrullus lanatus inoculated with Macrophomina pseudophaseolina.
Treatment/accessions | SLa (cm) | RLb (cm) | FSWc (g) | FRWd (g) | DSWe (g) | DRWf (g) |
AB07 | 111.5 b | 25.5 c | 20.0 b | 6.7 b | 2.8 a | 0.4 b |
AB24 | 139.5 a | 29.4 c | 14.7 c | 6.2 b | 2.6 a | 0.3 c |
AB26 | 112.9 b | 25.7 c | 10.7 d | 4.0 d | 2.1 a | 0.2 d |
AB36 | 122.0 b | 26.0 c | 16.6 c | 6.0 b | 2.5 a | 0.3 c |
AB39 | 163.9 a | 43.4 a | 24.9 a | 9.8 a | 3.4 a | 0.5 a |
AB40 | 58.5 c | 18.1 d | 4.2 e | 2.0 e | 1.2 b | 0.2 d |
AB41 | 47.0 c | 16.3 d | 6.5 e | 0.5 f | 1.3 b | 0.1 e |
AB44 | 69.1 c | 16.0 d | 6.7 e | 1.5 e | 1.4 b | 0.1 e |
AB50 | 63.0 c | 24.5 c | 5.2 e | 2.3 e | 1.2 b | 0.2 d |
AB51 | 156.5 a | 35.2 b | 21.4 b | 5.2 c | 3.0 a | 0.3 c |
AB52 | 115.2 b | 23.0 c | 12.1 d | 5.2 c | 2.5 a | 0.3 c |
AB55 | 113.2 b | 24.0 c | 16.0 c | 4.7 c | 2.0 b | 0.3 c |
Melon | 46.2 c | 21.0 d | 15.0 c | 2.3 e | 1.5 b | 0.1 e |
Watermelon | 83.0 c | 26.6 c | 22.5 b | 2.6 e | 3.0 a | 0.2 d |
CV (%) | 26.99 | 30.45 | 23.48 | 22.21 | 20.0 | 18.17 |
CV (%) = significant coefficients of variation; values followed by the same letter within columns do not differ statistically from each other by the Scott-Knott test (p ≤ 0.05). a Shoot length. b Root length. c Fresh shoot weight. d Fresh root weight. e Dry shoot weight. f Dry root weight.
For disease incidence, treatments AB24 (63.0%), AB39 (0.0%), and AB51 (50.0%) showed no significant difference compared to Watermelon (38.0%). Notably, among the Melon treatments, only AB39 (0.0%) exhibited a statistically different result remained unaffected by the pathogen, indicating its immunity to the disease (Table 3).
The reaction to M. pseudophaseolina revealed that nine out of the 12 Luffa spp. accessions exhibited a disease incidence of over 75% (AB07, AB26, AB36, AB40, AB41, AB44, AB50, AB52, and AB55) (Table 3). Remarkably, only accession AB39 remained unaffected by the disease. Comparatively, among the positive controls, Watermelon showed the least susceptibility. This aligns with findings by Negreiros et al. (2022), who observed higher disease incidence on melon (40% and 80% for isolates CMM4771 and CMM4801, respectively) compared to watermelon (0% and 40%, respectively), supporting the results of this study.
Regarding disease severity, Luffa spp. accessions AB40 (4.5), AB41 (5.0), AB44 (4.6), and AB50 (5.0) differed from Watermelon (0.5). However, when comparing treatments inoculated with M. pseudophaseolina to Melon (4.1), only AB39 (0.0) showed a statistically significant difference (Table 3).
Notably, the infection by M. pseudophaseolina in accessions AB41, AB44, and AB50 initiated around the 19th day after inoculation. Various structures such as microsclerotia and pycnidia were observed in close proximity to the plant's neck. Additionally, symptoms such as cracks in the hypocotyl and chlorosis on lower leaves appeared, ultimately resulting in the death of the plants (Fig. 2).
Based on the reaction classification proposed by Salari et al. (2012), AB39 demonstrated immunity to the pathogen, while AB55 exhibited a highly resistant reaction, akin to the positive control Watermelon. Treatments AB24 and AB51 were categorized as moderately resistant, whereas treatments AB07, AB26, AB36, and AB52 were deemed susceptible to the pathogen. Treatments AB40, AB41, AB44, AB50, and Melon were classified as highly susceptible (Table 3) (Fig. 3).
Hilal et al. (2000) conducted inoculation trials on L. aegyptiaca plants infected with M. phaseolina and reported the absence of symptoms. However, when combined with another pathogen, Pythium sp., visible symptoms emerged. Interestingly, the authors noted that the same M. phaseolina isolate (derived from L. aegyptiaca) exhibited high pathogenicity when introduced to various other crops, including cotton 'Giza 75', cucumber 'Amira 2', okra 'Costa Dourada', peanut 'Giza 4', pumpkin 'Balady', sesame 'Giza 32', soya 'Crawford', zucchini 'Eskandarani', and watermelon 'Giza 1'.
Wu et al. (2020) noted that the significant genetic variability within Luffa spp. may result in certain accessions possessing enriched resistance genes. These genes enhance the plants' capacity to withstand various environmental stresses, including water scarcity, temperature fluctuations, high humidity, and diseases.
Namisy et al. (2023) observed similar findings, noting variations in the reactions of different accessions when inoculated with Fusarium oxysporum f. sp. luffae. The authors attributed these differences to the influence of plant genotype on disease susceptibility and resistance.
For the biometric variable SL, treatments AB24, AB39, and AB51 demonstrated statistically superior performance compared to other treatments, with average values ranging from 139.5 to 163.9 cm, representing the highest recorded lengths. Conversely, treatments AB07, AB26, AB36, AB52, and AB55 significantly differed from both Melon and Watermelon, displaying lengths ranging from 111.5 to 122.0 cm. However, treatments AB40, AB41, AB44, and AB50 (ranging from 47.0 to 69.1 cm) did not exhibit significant differences compared to Melon and Watermelon (measuring 46.2 and 83.0 cm, respectively), indicating the shortest lengths.
Accession AB39 stood out statistically among all treatments for the variable RL (43.4 cm), FSW (24.9 g), FRW (9.8 g), and DRW (0.5 g), boasting the highest average values across these variables.
Conversely, for the RL variable, treatments AB40, AB41, AB44, and Melon showed significantly lower averages (ranging from 16.0 to 21.0 cm), indicating a notable reduction in this characteristic. Similarly, in terms of FSW, treatments AB40, AB41, AB44, and AB50 exhibited inferior values compared to other treatments, with averages ranging from 4.2 to 6.7 g. Regarding FRW, AB41 displayed the lowest average value (0.5 g) among treatments, indicating a greater reduction in the root system. With respect to DRW, the lowest recorded weight was 0.1 g for treatments TB41, TB44, and Melon.
Concerning DSW, treatments AB07, AB24, AB26, AB36, AB39, AB51, AB52, and Watermelon demonstrated statistically superior performance, ranging from 2.1 to 3.4 g. Conversely, treatments AB40, AB41, AB44, AB50, and AB55 exhibited average values ranging from 1.2 to 2.0 g, which differed significantly from the Watermelon treatment but not from the Melon treatment.
As Macrophomina spp. is a fungus naturally present in the soil and associated with its chemical and physical conditions, besides constantly interacting with other pathosystems, any strategy for disease management should aim to minimize alterations or manipulations of environmental and natural resources (Marquez et al., 2021). In this sense, pathogenicity studies play a crucial role in identifying resistant plant materials, as controlling Macrophomina spp. is inherently complex. Therefore, it is vital to implement one or a combination of control methods to mitigate the detrimental effects of phytopathogen attacks on vulnerable crops, thereby reducing inoculum pressure and the incidence of disease (Agrofit, 2024).
Grafting stands out as one of the most effective and environmentally friendly methods for controlling Macrophomina spp. in agricultural fields. Cohen et al. (2022) emphasized its success in select regions of Israel, where it has effectively managed this pathogen in melon and watermelon crops by utilizing pumpkin rootstock resistant to the disease. However, this approach necessitates careful selection of plant materials that not only align with target crops but also offer replicability and resistance to pathogens (Davis et al., 2008). In recent years, researchers have explored Luffa species as potential rootstocks for cucurbits such as pumpkin, cucumber, and melon (Li et al., 2016; Shahiba & Chacko, 2019; Nordey et al., 2020; Guo et al., 2023), making accession AB39 particularly promising for breeding programs aimed at developing resistant cultivars.
Moreover, it is noteworthy that this study marks the first documentation of Luffa spp. acting as an alternative host for M. pseudophaseolina, thus contributing significantly to our understanding of the interaction between M. pseudophaseolina and Luffa species. These findings offer valuable insights for managing the disease in other cucurbit crops. Additionally, accession AB39 exhibited the highest averages for RL and FRW among all treatments. As highlighted by Katuuramu et al. (2020), robust root development enhances nutrient and water absorption while mitigating severity of diseases transmitted by soil pathogens.