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The Control of White Root Rot of Apple Tree caused by Rosellinia Necatrix by Fluazinam and Prochloraz

Research Article | DOI: https://doi.org/

The Control of White Root Rot of Apple Tree caused by Rosellinia Necatrix by Fluazinam and Prochloraz

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Copyright: © permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Received: 30 November -0001 | Accepted: 26 March 2019 | Published: 05 April 2019

Keywords: Dematophora necatrix; chemical control; apple orchards

Abstract

White root rot disease caused by Rosellinia necatrix is destructive to many fruit trees, particularly apple and other deciduous crops. Replanting on infested soil  in  Israel  is  currently  not  practical   and   the   orchards   are  abandoned.  The   spread   of   R. necatrix    can  be avoided  using physycal or chemical methods. The effect of different fungicides was tested in a nursery on apple plants artificially infected. Without fungicide, 100% mortality of the plants was recorded 45±2 days after inoculation, compared with nursery plants treated with carbendazin, fluazinam and thiophanate methyl that wilted 80 days post inoculation.  Fluazinam is the only fungicide that improved plant viability during the 2013 and 2014 all growing seasons. Prochloraz improved plant viability in 2013 and 2014. However, in 2014, the significant efficiency was observed only until the end of August. Our study demonstrates, for the first time In Israel, that treatments with fluazinam and prochloraz in naturally- infested orchard soils prolong apple tree life in commercial plantations. Treatment with  thiophanate  methyl  can   control  R. necatrix with  limited efficiency.

10 µg mL-1a.i.

100 µg mL-1 a.i.

Fluazinam 50%

2,6-Dinitro- Anilines

a

Thiophanate methyl 70%

Table 1:Fungicides % inhibition in vitro. Colony growth of R. necatrix isolates Rn-E, Rn-D and Rn-L in PDA medium amended with 1, 10, and 100 µg mL-1 a.i. of fungicides. Observations were made 7 days after inoculation when the control colony covered the Petri plate (0% inhibition). Each value is the mean of three replicates.

QoI – Quinone outside inhibitors, MBC – methyl benzimidazole carbamates. PP – phenylpyrroles. DMI– demethylation inhibitors. The fungicide group was named according to the FRAC code list© 2013. In each column, number followed by Different letters indicate significant differences according to Tukey-Kramer (Honestly Significant Difference, HSD) test.

Variations between isolates were seen in captan application in the 10 and 1 µg mL-1 a.i. Yet, the difference between isolates was not constant between 3 experimental repeats.

    1. Nursery plants

Apple plants inoculated with R. necatrix were treated twice with fungicides as presented in Table 2.

  A.i. name fungicide

n

Live plants (%) 98 DPI (LSD)

Average days of living 169 DPI (HSD)

A

Table 2:Chemical treatments in artificially infected nursery apple plants. Inoculations were performed on 28 May 2013 and were assessed 98 and 162 days post inoculation (DPI).

Untreated plants used for control"-" Control (+) - inoculated plants. Control (-): plants not inoculated with R. necatrix.

Different letters indicate significant differences (P≤0.05) according to the Each pair student`s t, (Least Significant Difference, LSD) and Tukey-Kramer, HSD test.

In the control plants without chemical treatments, all plants died within 45±2 days after inoculation. Treatment with 15.5 mg/L of fluazinam was the most effective, with 100% of the plants remaining alive in September, with 125.6 days on average. Interestingly, only 80% of the plants were alive in September in the 31.0 mg L-1a.i. treatment, were one, but with no significant differences in the number of living days. In November, more plants wilted, while those treated with 86.8 mg/L of thiophanate methyl remained viable for a longer period of time, for 138 days on average. However, an increase in the concentration to 173.6 mg/L did not contribute to longer viability. No phytotoxic symptoms were observed in all treatments.

    1. Field experiments

3.3.1 Netua orchard

Only 6.3% and 13.3% of the control plants survived by the fall of 2013 and 2014, respectively (Table 3). In 2013, prochloraz and thiophanate methyl treatments significantly improved plant viability between 19/6/13 to 7/10/13 (contingency analysis, after Bonferroni correction, p<0.05, Figure 1). Three application of prochloraz treatments resulted in 80% viability with an average of 240.1±14.4 survival days, significantly more than the control treatment with an average of 102.6±14.6 survival days. Three application of thiophanate methyl treatments resulted in 53.8% plant viability with an average of 225.3±13.4 survival days. Results did not improve with 5 compared to 3 applications of prochloraz in terms of viability of the plants and in average living days. As a result, only 3 applications of prochloraz were applied in 2014. In 2014, prochloraz and thiophanate methyl significantly improved plant viability until 7 July, whereas only prochloraz significantly improved plant viability until 1 August, (contingency analysis, after Bonferroni correction, P≤0.05, except in 6/8/14, p=0.0253 that did not emerge as significant following the application of the Bonferroni corrections, Figure 1). Only prochloraz yielded significant response compared to the control, with 49 more living days on average (HSD, P≤0.05, Table 3). Neither of the fungicides improved plant vitality by the end of November (Figure. 1). In general, the block is not a significant factor in all experiments in Netua in 2013 and 2014.

3.3.2 Mas'ade orchard:

The viability rate in the control plants was higher relatively to Netua, with 30% and 60% of the plants surviving during the fall of 2013 and 2014, respectively. Plants began to show symptoms of wilting later during the winter, when the average vitality start to decrease (Figure 1). In 2013, fluazinam application significantly improved plant viability compared to untreated trees from 17/8/13 to 5/9/13 (Figure 1) and improved plant survival to 70% (Contingency Analysis, p=0.0114) with significantly  more survival days.

In 2014, fluazinam application increased the number of survival days significantly, and the viability of the plants increased to 90% (p=0.0285). This value did not emerge as significant following the application of the Bonferroni corrections. In 2013 and 2014, the carbendazim treatment applied 3 or 5 times enhanced plant viability, but did not result in significant differences from the control (Table 3). The effect of carbendazim applied 3 or 4 times during 2013 was not significantly different, and it was therefore applied only three times in 2014. The block was a significant (p<0.05) factor on the experiments in 2013, perhaps due to an unequal inoculum of the fungus in the soil, and the statistical analysis takes this into account. 

Treatment

Survival days ± SE

Survival days ± SE

Thiophanate methyl

225.3 ± 13.4 A

119.2 ± 10.7 AB

Prochloraz

240.1 ± 14.4 A

149.5 ± 15.5 A

Prochloraz (a)

223.6 ± 13.2 A

Control

102.6 ± 14.6 B

100.5 ± 13.5 B

102.3 ± 10.6 B

179.0 ± 12.5 B

Carbendazim

104.5 ± 10.0 B

189.4 ± 12.1 AB

Carbendazim (a)

120.8 ± 10.0 AB

60.0% (20)

Table 3: The effect of different fungicides on young apple trees in naturally infested soil in Netoa and Mas’ade.

The treatments in 2014 were given on the background of the treatments 2013 results. All treatments were given 3 times, except for prochloraz and carbendazim in 2013, that were given 5 times (a). Viability was calculated as the number of healthy plants out of all tested plants (n).

P-values indicate differences between the treatment and the control (Pearson test)

* Significant differences from the control (P≤0.01) using Contingency Analysis with Bonferroni correction.

** Significant differences from the control (P≤0.05) using Contingency Analysis with Bonferroni correction. Different capital letters indicate significant differences in the number of living days according to HSD, except in Mas’ade 2014, where different letters indicate significantly different LSD.

References

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