Detection and control of leaf blotch and stem end rot of strawberry caused by Gnomoniopsis fructicola

Rajendra Gounder

Gnomoniopsis leaf blotch and fruit stem end rot

Gnomoniopsis fructicola (syn. Gnomonia comari)• leaf blotch and spots, stem end rot (SER) on fruit

Economic fruit losses due to SER during unseasonal weather in the early 1990s & in late 2000s

Victorian strawberry runners implicated as the source

Victoria is major supplier of runners in Australia

Research in 1990’s funded by TCSRG Co-op, DPI & HAL; Current program funded by TCSRG Co-op

Zythia fragariae(anamorph)

Life cycle of Gnomoniopsis fructicola Conidia Ascospores

Acervulus containing conidia

Perithecia and ascus containing

Ascospores

Asexual Sexual

Infects through stomata and wounds

The fungus over-winters in the infected leaves and petioles

Conidia and ascospores are splash

dispersed

G. Fructicola(teleomorph)

Strawberry runner multiplication and certification Scheme

NUCLEUS

MOTHER

FOUNDATION

COMMERCIAL

FRUIT

Generations

Quarantine AQIS

Tissue culture explants Quarantine screenhouses

Runners in field nurseries

Runners on grower farms

Fruit production

Plantlets in screenhouses

Multiplication Breeding programs

Germplasm

Research in 1991 to 1995

Systematic surveys• Leaf blotch Nucleus and Foundation generation• Leaf blotch Mother and Runner generations • Incidence and severity varied • Leaf blotch most common on Pajaro and Chandler,

least on Selva, Parker and Red Gauntlet, intermediate on Tioga

• Isolation- high incidence of systemic infection of runner plants

• Incidence of fungus not correlated with disease incidence and severity

Incidence of G. fructicola in runners in cool storage

Table 1 A comparison of the predicted means for the incidence of detection of Gn (based on regression analysis) from petioles of 1991/92 Foundation and Mother generation strawberry

runners from cool storage Foundation runners: estimated infection rates for the 1st segment (crown end) of the oldest petiole Mother runners: estimated infection rates for the 1stsegment (crown end) averaged over all petioles

Cultivar Incidence of detection of Gn (%) Foundation Mother Chandler 20 aA 76 cd Pajaro 31 ab 66 c Parker 71 bc 33 a Selva 27 a 45 b Redgauntlet 82 c 91 e Tioga 42 ab 88 de Anumbers with the same letter do not differ statistically (P>0.05) from each one another

Gnomoniopsis fructicola in the runner multiplication scheme

Incidence of detection (%) of G. fructicola in petioles of runner plants in the different generations of the strawberry runner multiplication scheme

(A Sampled from cool storage, B Sampled from untreated controls in fungicide field trials)

Generation 91/92 Pajaro

92/93Pajaro

93/94Pajaro

94/95 Pajaro

08/09 Festival

09/10 Festival

Nucleus - 88 3 0 - -Foundation 21 0 8 0 0A 29A

Mother 89 40 62 53 33A 28A

Runner 31A 84B 80B 64B 12A 36A

Pathogenicity of G. fructicola

Effect of different temperature regimes on disease incidence in plantlets artifically inoculated with Gnomoniopsis fructicola

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

6 7 8 9 10 11 12 13 14

Days after inoculation

Inci

denc

e of

leav

es w

ith le

af

spot

(%)

10ºC10ºC-16ºC10ºC- 26ºC16ºC16ºC - 26ºC26ºC

Disease management with fungicides

Table 1 Trial 1, 1992/93 - Effects of fungicide treatments on the severity of leaf blotch on mother and runner plants, on the incidence of detection of Gn in petioles and on the dry weight of foliage of runners of cv. Pajaro at harvest

Fungicide treatment

Active ingredient Rate of application (/100 L)

Leaf blotch severityA No. runner plants with Gn (out of 10)

Dry weight of foliage (kg/plot)

Mother plantsB Runner bedsC 6/1/93 31/3/93 18/5/93 Control - 0.79 0.49 0.17 8.4 1.3 Thiram 800 800 g/kg thiram 150 g 0.77 0.46 0.17 6.4 1.1 Euparen 500 g/kg

dichlofluanid 200 g 0.20 0.41 0.12 4.4 1.6

Octave WP 462 g/kg prochloraz 200 g 0.08 0.16 0.02 2.6 1.6 Foli-R-Fos 200 200 g/L potassium

phosphonate 500 mL 0.70 0.43 0.13 8.8 1.2

Bayfidan 250 EC 250 g/L tridimefon 40 mL 0.27 0.20 0.08 7.2 1.5 Rovral 500 g/kg iprodione 100 mL 0.30 0.57 0.21 8.0 1.8 Benlate 500 g/kg benomyl 50 g 0.27 0.38 0.11 7.4 1.4 Bravo 500 g/L

chlorothalonil 230 mL 1.05 0.50 0.16 8.6 1.2

ZK 100309 400 g/L pyrimethanil

75 mL 0.21 0.47 0.18 9.2 1.3

P value - - 0.006 <0.001 0.002 <.001 <0.001 l.s.d. (P=0.05) - - 0.53 0.12 0.08 2.0 0.3 A Leaf blotch severity rating on a scale of 0-3 BIndividual plants CAssessed in two 40cm x 40cm quadrants/plot n.s.F-test not significant at P=0.05

Evaluation of fungicides in vitro

* s.e. = standard error

Effect of fungicides on radial growth in Petri plate assays (Agar amended with fungicides)

Treatment Inhibition of fungal growth (%) Grow-on test

Prochloraz (positive control) 100.00 No regrowth

Azoxystrobin+ Difenoconazole 100.00 No regrowth

Pyraclostrobin 100.00 Regrowth

Trifloxystrobin 87.0 (s.e.* 6.4) Regrowth

Boscalid + Pyraclostrobin 100.00 Regrowth

Cyprodinil + Fludioxinil 100.00 Regrowth

Untreated (negative control) 0.00 Regrowth

Evaluation of fungicides in the fieldIncidence of blotch and spots on leaves of strawberry plant following application of fungicides

0.0

5.0

10.0

15.0

20.0

25.0

Azoxystrobin + difenoconazole

Pyraclostrobin Prochloraz Rotation Trifloxystrobin Pyraclostrobin +boscalid

Cyprodinil + fludioxinil

Control

Dis

ease

inci

denc

e (%

)

Recommendations (90’s)

• Routine sampling in scheme• Strict hygiene• Fungicide program (prochloraz)• More options for fungicide program• More research on biology of fungus

Current situation (2000)• Incidence same as 90’s in multiplication scheme • New fungicides look promising for use with prochloraz but

require more work• Continue with 90’s recommendation• More research on fungus, disease development and

environmental factors

AcknowledgementsTeam

• Dolf de Boer• Jan Strawhorn• Scott Mattner• Philip Keane• Don Hutton• Ian Porter• William Spatari

Funding• TCSRG Co-op (1990’s and 2000)• Department of Primary Industries• Horticulture Australia (1990’s and 2000)