Evaluating host resistance to Macrophomina crown rot in strawberryJonathan Winslow1, Mark Mazzola2, Gerald J. Holmes1 and Kelly L. Ivors1

1Strawberry Center, California Polytechnic State University, San Luis Obispo; 2USDA ARS, Wenatchee, WA

IntroductionMacrophomina crown rot, caused by the soilbornefungus Macrophomina phaseolina, is an emergingpathogen in California strawberry production (Koikeet al., 2016). M. phaseolina can be difficult to managedue to its persistence in soil and crop residues asmicrosclerotia (Islam et al., 2012). Host resistance willbe a critical tool for managing this disease in thepost-methyl bromide era. The objective of thisresearch was to evaluate the resistance of a widerange of currently available cultivars and eliteselections to Macrophomina crown rot.

Results

Discussion

Materials and Methods

All breeding programs contained both tolerant andsusceptible germplasm to Macrophomina crown rot.The plant response observed in this trial was inagreement with the literature (Zveibil et al., 2012)that damage due to Macrophomina crown rotoccurred late in the season and was exacerbated bywarm temperatures during the months of June andJuly. This inoculation method provided consistent,but not overwhelming, pressure for field evaluationof host resistance to M. phaseolina. This data canserve as both a guide to growers for managingMacrophomina crown rot, and for the developmentof new resistant cultivars for existing breedingprograms.

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23.523.6

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27.528.8

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30.030.0

30.430.6

33.234.2

35.035.0

36.336.3

36.537.537.538.0

40.040.0

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40.341.3

42.545.0

46.346.3

46.547.5

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50.050.6

52.052.5

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56.960.0

61.361.8

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74.274.6

76.378.8

81.589.9

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0 10 20 30 40 50 60 70 80 90 100

OSCEOLA (47)MANRESA (43)

UC- V (28)UC- G (13)PSI- D (69)UC- R (24)

UC- B (8)UC- F (12)UC- U (27)DR- A (53)

MEGAN (45)GRENADA (1)

PSI- B (67)UC- Z (32)

PL 02-32 (87)UC- I (15)

UC- M (19)LAREDO (42)PS 9271 (64)

UC- O (21)UC- N (20)

BG 6.3024 (58)PSI- C (68)PSI- G (72)UC- W (29)

ALAFIA (33)DR- F (51)UC- C (9)

DR- D (56)AMADO (34)

UC- S (25)UC- E (11)

PETALUMA (3)ENCINITA (41)MARQUIS (44)

SAN ANDREAS (90)UC- T (26)ANYA (35)

BG 4.352 (60)UC- Q (23)

BIG SUR (36)UC- H (14)

UC- A (7)BG 4.367 (59)BG 1975 (63)PL 09-11 (86)SABRINA (83)

UC- P (22)BG 3.324 (61)DEL REY (39)BG 959 (62)

LC- F (82)UC- K (17)

MYSTIC (46)DR- G (52)

PORTOLA (6)PL 05-100R (85)FRONTERAS (2)

PSI- F (71)UC- L (18)DR- C (55)LC- C (79)

PSI- A (66)PASADENA (48)

PSI- E (70)ALBION (37)

PE 7.2059 (65)DR- E (57)LC- E (81)

UC- D (10)ALBION (4)

CELINE (38)LC- B (78)

PL 09-49 (84)LUCIA (75)LC- D (80)

PILGRIM (50)PASILLO (49)ODESSA (54)

EL DORADO (40)SWEET ANN (73)

MONTEREY (5)UC- X (30)

SCARLET (76)LC- A (77)UC- Y (31)

FESTIVAL (89)RUBY JUNE (74)

UC- J (16)

Plant mortality (%)

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Average plant mortality (%) due to Macrophomina crown rot as of July 24, 2017

University of Florida

University of California Davis

Plant Sciences

Planasa

Lassen Canyon

Driscoll’s

• A replicated field trial was conducted to evaluate90 cultivars and elite selections for resistance toMacrophomina crown rot.

• Strawberry germplasm was selected from sixpublic and private breeding programs: UniversityCalifornia Davis, University of Florida, Driscoll’s,Plant Sciences, Planasa and Lassen Canyon.

• The trial was conducted at Cal Poly in San LuisObispo during the 2016-17 growing season.

• The experimental design consisted of arandomized complete block with four replicateplots per cultivar; each plot contained 20 plants.

• Plants were artificially inoculated with 5 grams ofa M. phaseolina infested cornmeal-sand mix atthe crown-root interface.

• Plant mortality was assessed every four weeks,then every two weeks once symptoms wereobserved.

• Plant mortality was distinguished when plantfoliage was 100% necrotic.

A B

CFigure 1. A. Initial symptoms of Macrophomina crown rot include wiltingand plant discoloration. B. Microsclerotia of M. phaseolina surrounding thestele of an infected root. C. Cross section of an infected plant; microsclerotiacan be seen in the vascular tissue as black flecks (red arrow). D. Artificialinoculation of transplant using cornmeal-sand inoculum.

Figure 2. Average percent plant mortality due to Macrophomina crown rot as of 24 Jul 2017. Error barsrepresent the standard error of the mean. Statistical differences by pairwise comparisons not shown.*Average of three replicate plots rather then four.

*

A BFigure 3. A. Partially resistant cultivar Manresa; B. Susceptible cultivar Ruby June. Photos taken on 1Aug 2017 at the end of the growing season.

• The first wilt symptoms due to infection by M.phaseolina were observed in March, roughly 210days after planting.

• The majority of plant mortality occurred after 15Jun, when air temperatures exceeded 32oC forseveral days.

• Of the cultivars tested, a wide range ofsusceptibility was observed.

• Elite selection UC-J and cultivar Ruby June wherethe most susceptible genotypes to crown rot,with more than 90% mortality by 24 Jul 2017.

• Elite selection UC-V and cultivars Manresa andOsceola were the most tolerant genotypes toMacrophomina crown rot, with less then 5%mortality by 24 Jul 2017.

D

Acknowledgements and ReferencesFunding for this project was provided by the California StateUniversity Agricultural Research Institute (ARI), the CaliforniaStrawberry Commission, and the USDA-ARS western region,Area Wide Project: 5350-21220-001-206.

• Islam, M.S., Haque, M.S., Islam, M.M., Emdad, E.M., Halim,A., Hossen, Q.M.M., Hossain, M.Z., Ahmed, B., Rahim, S.,Rahman, M.S. and Alam, M.M. 2012. Tools to kill: genomeof one of the most destructive plant pathogenic fungiMacrophomina phaseolina. Bmc Genomics 13:493-509.

• Koike, S.T., Arias, R.S., Hogan, C.S., Martin, F.N. andGordon, T.R. 2016. Status of Macrophomina phaseolina onstrawberry in California and preliminary characterization ofthe pathogen. International Journal of FruitScience 16:148-159.

• Zveibil, A., Mor, N., Gnayem, N. and Freeman, S. 2012.Survival, host–pathogen interaction, and management ofMacrophomina phaseolina on strawberry in Israel. PlantDis. 96:265-272.

Results Continued