Themls J. Michalltdes University of California, Berkeley Kearney Agricultural Center, Parlier, CA

Robert A. Spotts Oregon State University Mid-Columbia Agricultural Research and Extension Center, Hood River

Postharvest Diseases of Pome and Stone Fruits Caused by Mucor piriformis in the Pacific Northwest and California

In the Pacific Northwmt, pome fruits, i.e., pear ( P y m comrnunis L.) and apple (Mdus domesiica Borkh.), occupy ap- proximately 87,000 ha, whereas stone fruits, including peach (Prunus persica (L.) Batsch), nectarine (P, persica var. nectarina (Aiton) Maxim.), plum and prune (P. domesrica L.), cherry(P. avium L.), and apricot (P. armeniaco L.), occupy only 9,845 ha. In contrast, in California, stone fruits occupy 94,000 ha and pome fruits occupy only 13,000 ha, although since the 1980s this acreage has been increasing.

Losses of pome and stone fruit from decay that develops in cold storage often depend on conditions of storage. Tem- peratures below 5 C prevent brown rot and Rhizopus or Gilbertella rot on stone fruit and reduce Botrytis and Penicillium rot on pome fruit, but other rots caused by fungi that can tolerate low temper- atures still result in losses in storage. Among these, Mucorpiriforrnis Fischer has become a serious threat for fruit in cold storage in the Pacific Northwest and is sometimes a problem for the California stone-fruit industry.

Until recently, Mucor spp. were of relatively minor importance as posthar- vest pathogens. In the last two decades, however, they have caused serious decay of strawberries (Fragaria X ananassa Duchesne), pears, agptes, guavas (Psid- ium guajavo L.), peaches, nedahnes, and vegetables, such as tomato (lycopersi- con escuIenrum MilIer) and sweet potato (Ipornoeo boraras (L.) Lam.). In Europe, M. piriformis and other Mucor spp., such as M. mucedo L.: Fr., M. racernosus Fres., and M. strictw Hagem, occasion- ally have been reported as causing rot

of pome fruits (3,B). During 1970-1980, Mucor rot caused major losses in pears and apples in the Pacific Northwest (2). Because chemical control of this disease is not possible, significant losses of pome fruit in cold storage occur each year. Mucor rot of pears and apples in the Pacific Northwest and Canada and of stone fruit in California is caused only by M. piriformis; therefore, this discus- sion refers excEusively to this species. M. ppirifarmis, initially described by A.

Fischer in 1892, was first reported as. a cause of fruit decay in 1895 (31). Subsc- quent reports that cover approximately a century on Mucor rot of pome and stone fruit are listed in Table 1. In 1975 (2), a Mucor rot outbreak on pame fruit occurred in the mid-Columbia area of Oregon and Washington. In 1977, Mucor rot caused significant losses of stone fruit in California, when an unusuaI amount

! I. A cent1 fruit throu

&*" .-m,I1

15 Pea API

,8 API .O Pea '2 Pea '3 st0 ' 5 Pea ,- -

ury of rep0 nhout the v

- --I repor+--' Awtcted fruit -

189 193 193 194 197 191 197 197, pea 1979 Pea I980 Pea I982 Pea 1987 Pru t 989 Asi, 1990 Pea

r I

ne fruit r . - cn- ch, nectarit ch, nectarir r, apple m- I,"

an pear, ap: ch

m on Mut vorld

ple, plum

of decay developed during cold-tern- perature (approximately 5 C) transit of fresh-market peaches from California to markets in the eastern United States and of nectarines shipped from Chile to California.

From 1962 to 1990. several Mucor spp.. including M, circimelloides van Tieghem, M. racernosus. M. plumbeus Bonorden, and M. hiemalis Webrner. were isolated from stone fruit in the field and in cold storage in California, but only M. piriformis caused serious fruit losses in cold storage. During 1988-1989, M. piriforrnis was commonly isolated from infected Asian pears, Fuji apples, and plums, all grown in California.

Symptomatology Infection occurs through the stem end,

the calyx, or puncture wounds. In 1988 we atso observed Mucor rot initiating

:or rot caul

Ltxatlon

Pilze, Germany Washingtan, USA Northern Ireland Washington, USA British Columbia, Canada Maryland, USA Oregon and Washington, USA Pennsylvania, USA Maryland, USA California, USA Victoria, Australia California, USA Californi, British Cs

a, USA olumbia. C. anada

5 and

I 24

(TJ h 3;

I T Y l

(TJ I 2;

'Pathogen was i 'Identified by.thc ursl aurnur.

I Mucor aft - -

w a f e r Nau mov, a synl

* 1990 The Americsn Phytopathologlcal 3mleiy

Plant Disease/August 1990 537