Developing pest resistance mechanisms of grape in the Baltic shore

Grape cultivation in cool maritime zones faces unique pest and disease pressures that differ markedly from those in traditional Mediterranean viticultural regions. In the context of the Baltic Shore’s climate, where high humidity and moderate summers favor fungal pathogens over insect pests, this research examined pest resistance mechanisms in four table grape cultivars Thompson Seedless, Flame Seedless, Bangalore Blue, and an Assam hybrid grown at the Guwahati School of Plant Sciences, India, from February 2022 to January 2023. Volatile Organic Compound (VOC) profiling by headspace GC-MS identified 38 compounds in leaf tissue, with linalool and beta-ocimene showing the strongest negative correlations with thrips density (r=-0.71 and -0.64, respectively). Crop rotation in the vineyard floor with mustard reduced soilborne fungal inoculum by 27 percent compared with bare fallow. Combining ability analysis from a 4 × 4 half-diallel showed significant GCA for berry weight and SCA for downy mildew resistance. Post-harvest quality after 21 days of cold storage varied by cultivar, with Bangalore Blue retaining 94 percent of initial anthocyanin content versus 78 percent for Thompson Seedless. Water use efficiency under deficit irrigation at 60 percent ETc was 11.4 kg/m³, compared with 7.8 kg/m³ at full irrigation.

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VOC-Pest RelationshipClose ×

AI-generated conceptual illustration (Grape leaves and thrips). It explains the idea and does not show study data.

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Flame SL: Total VOCs (µg/g/h) vs β-Ocimene (µg/g/h) vs Thrips/ leafClose ×

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Bangalore Blue: Total VOCs (µg/g/h) vs β-Ocimene (µg/g/h) vs Thrips/ leafClose ×

Replotted from Table 1 (page 2) of the original paper. Every bar is the paper's own table value.

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Introduction

In a regional context where climate projections suggest that grape cultivation could expand northward into cool maritime zones within the next two decades, understanding pest resistance in these environments has become newly urgent [1] . Grapevine (Vitis vinifera L.) hosts more than 50 arthropod pest species and dozens of fungal pathogens worldwide, but the pest complex shifts dramatically with latitude and humidity [2] . Volatile organic compounds emitted by grapevine leaves function as direct deterrents against some herbivores and as attractants for natural enemies of others [3] . Terpenes like linalool and ocimene have documented repellent activity against thrips and mites in several horticultural crops [4] . Crop rotation rarely discussed in perennial fruit systems can be applied to vineyard floor management by alternating cover crop species to disrupt soilborne pathogen cycles [5] . Combining ability analysis through diallel crosses allows breeders to distinguish between additive (GCA) and non-additive (SCA) genetic effects for resistance traits [6] . Post-harvest quality retention, particularly of anthocyanins and other phenolics, determines whether disease-resistant cultivars can also meet market quality standards [7] . This research combined VOC profiling, crop rotation trials, genetic analysis, and post-harvest evaluation to build a comprehensive picture of pest resistance potential in grape under cool-humid conditions [8] .

Material and Methods

Material and Methods

Material

Four table grape cultivars were maintained on own-root vines trained to a Y-trellis system in a rain shelter at the Guwahati School of Plant Sciences (26.14°N, 91.74°E). Vineyard floor treatments included bare fallow, mustard cover crop (Brassica juncea, incorporated at 50% flowering), and ryegrass cover crop. Irrigation regimes were full (100% ETc) and deficit (60% ETc) via drip emitters. A 4 × 4 half-diallel crossing scheme produced six F₂ families evaluated for berry weight, TSS, and downy mildew resistance (scored 0-9). Research ran from February 2022 to January 2023, with four replications per treatment [9] .

Methods

VOCs were collected from intact leaves by dynamic headspace sampling onto Tenax TA traps and analyzed on a GC-MS (Agilent 7890B/5977A) with a DB-5ms column. Compounds were identified against NIST 17 library spectra. Thrips were counted on 20 randomly selected leaves per vine weekly. Soil fungal inoculum was estimated by dilution plating on PDA at four vineyard floor positions per treatment. Post-harvest evaluation stored clusters at 2°C and 90% RH for 21 days, measuring weight loss, firmness, TSS, acidity, and anthocyanin by pH-differential method. Combining ability was analyzed by Griffing's Method 4, Model I. AMMI (Additive Main Effects and Multiplicative Interaction) analysis was applied to cultivar × environment (irrigation × floor management) using GenStat 21. Water use efficiency was calculated as marketable yield per cubic meter of water applied [10] . The plot reveals the expected sugar-acid trade-off across cultivars and treatments. Larger bubbles (higher aroma) clustered in the moderate-sugar, moderate-acid zone, suggesting that extreme ripeness or underripeness both reduce perceived aroma intensity. Environment 3 (deficit irrigation + mustard rotation) produced the highest anthocyanin and TSS values, while Environment 4 (full irrigation + bare fallow) ranked lowest for most quality traits. AMMI analysis confirmed significant cultivar × environment interaction (p<0.01) for anthocyanin content.

Results

Results

Discussion

The strong inverse relationship between linalool emission and thrips density (r=-0.71) supports the hypothesis that terpene volatiles function as constitutive chemical defenses in grape leaves [3] . Bangalore Blue, a Vitis labrusca hybrid, likely inherited stronger VOC production from its American grape parentage, which evolved under heavier herbivore pressure than V. vinifera in the Mediterranean [2] . For breeding programs, VOC profiling could serve as an earlygeneration screening tool for pest resistance, avoiding the need for labor-intensive field inoculation trials [4] . Mustard rotation reduced soilborne fungal inoculum by 27 percent, consistent with the biofumigation effect of glucosinolate breakdown products released during mustard residue decomposition [5] . This is a practical, low-cost intervention for cool-humid vineyards where soilborne diseases are a persistent problem. Combining ability analysis showed significant GCA for berry weight (Bangalore Blue as best combiner) and SCA for mildew resistance (Bangalore Blue × Assam Hybrid as the best specific cross), confirming that resistance involves both additive and nonadditive genetic mechanisms [6] . Post-harvest anthocyanin retention was cultivar-dependent: Bangalore Blue's 94 percent retention after 21 days of cold storage far exceeded Thompson Seedless at 78 percent. This stability likely reflects differences in anthocyanin acylation patterns, since acylated anthocyanins are more resistant to degradation than their non-acylated counterparts [7] . Water use efficiency under deficit irrigation improved by 46 percent with only a 12 percent yield penalty, making it an attractive option for water-limited settings [11] .

Conclusion

VOC profiling revealed that grape cultivars with higher linalool and beta-ocimene emissions experienced significantly lower pest incidence, identifying a chemical defense axis that could guide resistance breeding. Mustard rotation as a vineyard floor management tool reduced soilborne fungal pressure by 27 percent. Combining ability analysis pointed to Bangalore Blue as a valuable parent for both berry weight and disease resistance. Post-harvest anthocyanin retention varied widely among cultivars, with Bangalore Blue maintaining 94 percent over 21 days of cold storage. Deficit irrigation at 60 percent ETc improved water efficiency substantially. Together, these findings support a multi-pronged approach to grape pest management in cool maritime environments.

Figures and tables from the paper

Cultivar	Total VOCs (µg/g/h)	Linalool (µg/g/h)	β-Ocimene (µg/g/h)	Thrips/ leaf	Mildew (0–9)
Thompson SL	3.42 ± 0.28	0.41 ± 0.04	0.23 ± 0.03	8.7 ± 1.2	6.4 ± 0.7
Flame SL	4.18 ± 0.34	0.58 ± 0.05	0.37 ± 0.04	5.3 ± 0.9	4.8 ± 0.5
Bangalore Blue	5.87 ± 0.41	0.84 ± 0.07	0.62 ± 0.05	2.8 ± 0.6	2.1 ± 0.3
Assam Hybrid	5.24 ± 0.37	0.72 ± 0.06	0.51 ± 0.04	3.4 ± 0.7	2.7 ± 0.4

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Volatile organic compound emissions and pest incidence across four grape cultivars (mean across irrigation regimes)

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Bubble plot of total sugars versus titratable acidity, with bubble size proportional to aroma intensity score

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Heatmap of five quality traits across four simulated environments (irrigation × floor management combinations)

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