Management of stubby root nematodes (Trichodorus and Paratrichodorus spp.), associated with Docking disorder of Sugar beet (Beta vulgaris L) using brassica and non-brassica cover crops
Mwangi, N.G. (2025) Management of stubby root nematodes (Trichodorus and Paratrichodorus spp.), associated with Docking disorder of Sugar beet (Beta vulgaris L) using brassica and non-brassica cover crops. Doctoral thesis, Harper Adams University.
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Abstract
This study investigated the impact of utilizing cover crops in the suppression of stubby root nematodes (Trichodorus and Paratrichodorus spp.) — SRN, and the subsequent effects on quality and quantity of sugar beet (Beta vulgaris). The active compounds associated with some of these cover crops were also evaluated for their potential nematicidal/nematostatic effects on SRN in in-vitro assays. Pure Isothiocyanates (ITCs), associated with brassicas, namely 2-phenylethyl (PEITC), allyl (AITC), and sulforaphane (SITC) were tested at different concentrations (1.625, 3.125, 6.25, 12.5, 25, and 50 μg ml−1). Effect on nematode mobility was evaluated after 24, 48, and 72 h, and mortality of SRN was assessed after 48 h of incubation in distilled water following ITC treatment. The mortality for all ITCs at all tested concentrations was significantly higher than the controls, distilled water, and 1% DMSO. The concentration and type of ITC had a significant effect on SRN mobility and mortality, while an increase in exposure time did not significantly increase the immobility of SRN. The average 24-hour ED50 (dose resulting in 50% immobility) for SRN were 7, 5, and 44 μgml−1, and the average LD50 (dose resulting in 50% mortality) after 48 h of recovery in distilled water was 7, 11, and 24.3 μgml−1 for PEITC, AITC and SITC, respectively. The efficacy of cover crops under field conditions was tested at three locations in England: Bury St Edmunds, Suffolk (site 1) and Docking, Norfolk (site 2) and Tibberton Grange, Shropshire (site 3). Brassica and non-brassica cover crops were tested. The cover crops included Indian mustard (Brassica juncea), oilseed radish (Raphanus sativus), daikon radish (Raphanus sativus subsp.Longipinnatus), grass with endophyte (E+), grass without endophyte (E-) (Festulolium loliaceum), Italian rye grass (Lolium multiflorum), Phacelia (Phacelia tanacefolia), and opium poppy (Papaver somniferum), stubble turnips (B. rapa), strigosa oats (Avena strigosa), clover (Trifolium alexandrinum), vetch (Vicia sativa) and vitality mix. At site 1, plots sown with brassica cover crops, specifically Indian mustard, and oilseed radish, exhibited significantly lower SRN reproduction factor (Rf) (P<0.05) compared to the fallow control and daikon radish. In site 2, plots sown with Italian rye grass, Indian mustard, grass without endophyte (E-), or left fallow and undisturbed had a significantly higher Rf (P<0.05) compared to plots with Phacelia, opium poppy, and disturbed or sterile fallows, while in site 3, clover had significantly higher multiplication rate of SRN compared to all the other cover crops. It was four times higher than the vitality mix, three times than radish and vetch and twice higher than oats and stubble turnips. The vitality mix had the lowest SRN multiplication rate. Results from assessment of sugar beet quantity and quality parameters post cover crops indicated that sugar beet root fanging (%) and root soil tare (%) was significantly lower in cover crops and fallow plots with lower SRN Rf values, such as Phacelia, opium poppy, sterile fallow, and disturbed fallow. Environmental factors like rainfall and soil temperature also significantly impacted SRN densities at different sampling points, where SRN decreased with decreasing rain and increasing soil temperatures. The findings suggest that certain cover crops can impede SRN multiplication, despite SRN's polyphagous nature. Furthermore, factors such as weed occurrence, soil temperature, rainfall, and soil disturbance significantly affect SRN densities under field conditions. Following the observed difference in SRN reproduction between grass with endophyte (E+) and grass without (E-) in the field trial, in-vitro experiments with shoot and root extracts were conducted to test the sensitivity of SRN to the associated compounds. Both E+ and E- extracts obtained from shoots and roots had the ability to immobilise SRN, despite the presence of the endophyte. However, a comparison of the LD50values revealed that the presence of the endophyte significantly impacted the mortality of SRN. The LD50 values of E+ extracts were lower (P<0.05) than E- extracts across all ages. Specifically, the LD50 value for shoot extracts of endophyte grass (E+) was significantly lower at 8 weeks old compared to all other ages, being twice as low as 12 weeks, 11 times lower than 16 weeks, and six times lower than 20 weeks extracts. The LD50 for E+ root extracts at 20 weeks were half that of 12 weeks, although not significantly different from 16 weeks. In contrast, the LD50 values of root extracts from grass without endophyte followed a different pattern, increasing with the age of the grass. The LD50 value for 20-week-old plants was five times higher than that of 12- and 16-week-old plants. No mortality was recorded in the 8-week-old root extracts of both E+ and E- grass. The LD50 values also revealed that root extracts from E+ grass were more potent than those from E- grass, with the LD50 values at 12 weeks being twice as low for E+ compared to E-, and nearly 50 times lower at 20 weeks when compared to E-. Age of the grass significantly affected loline concentration in both shoots and roots, where the concentration increased with increasing age in both shoots and roots. On the other hand, the total flavonoid content (TFC) and total phenol content (TPC) in shoot extracts decreased with age in both E+ and E- grass, with no significant differences recorded between E+ and E- grass. A negative correlation between shoot biomass and TFC (R = -0.94), and between shoot biomass and TPC (R = - 0.67) and root biomass and TPC (R = -0.79) was recorded. Upon bruising and wounding of endophyte grass (E+), the change in composition and total concentration of lolines was recorded. Specifically, NFL, NAL, and NANL were present in the 3, 7, and 11 dpb extracts but absent in the 30 days post bruising (dpb)extracts and the control. Total loline alkaloid content in the shoot extracts at 3, 7, and 11 dpb was significantly higher compared to the 30 dpb extracts and the control unbruised. This translated into lower LD50 values for shoot extracts from regrowth tissue at 3-, 7-, and 11-days post bruising (dpb) when compared to 30 dpb extracts and the control. In conclusion, this study has demonstrated potential of using brassica cover crops and non-brassica cover crops for managing SRN.
| Item Type: | Thesis (Doctoral) |
|---|---|
| Divisions: | Agriculture and Environment (from 1.08.20) |
| Depositing User: | Miss Anna Cope |
| Date Deposited: | 16 Sep 2025 10:26 |
| Last Modified: | 16 Sep 2025 10:26 |
| URI: | https://hau.repository.guildhe.ac.uk/id/eprint/18254 |
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