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Rhizopus Soft Rot of Sweetpotato

Scot Nelson Department of Plant and Environmental Protection Sciences

Growers in Hawai'i produce a number of sweetpotato varieties with

different skin and flesh colors. Perhaps the most important and widely grown
variety, and one that is exported to the U.S. mainland, has purplish flesh inside the
storage roots of the plant and is known as the Okinawan purple sweetpotato.
Several significant, common postharvest diseases of similar appearance threaten
to reduce Okinawan sweetpotato production and profits for Hawai'i growers,
marketers, and exporters. The pathogens that cause these diseases can occur alone
or together and infect plants within the same areas of the sweetpotato field. The
major postharvest diseases of the Okinawan sweetpotatoes in Hawai'i include
Ceratocystis black rot, Java black rot, Rhizopus soft rot, and scurf. This
publication describes one of the most costly postharvest diseases of
sweetpotatoes, Rhizopus soft rot. When the infection is restricted, it is called ring
rot or collar rot. The symptoms of the disease are similar on other sweetpotato
varieties grown in Hawai'i. (synonym Ipomoea fastigiata Choisy), of the plant
family Convolvulaceae, is a tuberous-rooted perennial At a grocery store on
Hawai'i, Okinawan purple sweetpotatoes show symptoms not only of Rhizopus
rot but of Java black rot and scurf. It is common to see several postharvest
diseases of sweetpotatoes in the same batch.

The severity of these diseases can be reduced using the integrated

management methods similar to those described in this publication for Rhizopus
soft rot. UH-CTAHR Rhizopus Soft Rot of Sweetpotato PD-68 - Feb. The fungi
causing disease of sweetpotato worldwide include several Rhizopus species,
Rhizopus nigricans = Rhizopus stolonifer, also known as the common bread mold,
Rhizopus sp. and Rhizopus oryzae. In Hawai'i, the disease can occur wherever
sweetpotatoes are grown or processed. Sites of infection are primarily wounded,
necrotic storage root periderms (wounded sweetpotato "skins"). These sites are
usually the broken tips of sweetpotatoes damaged during harvest, holes in the
periderm caused by tools or insects such as weevils, or bruises or wounds created
by overly rough handling of sweetpotatoes after harvest and during processing.
Uncured sweetpotatoes are more prone to damage than are cured sweetpotatoes.
Curing is a process that creates wound periderm, a scarlike tissue that seals
wounds and reduces infections. Symptoms Symtpoms may begin in any wounded
or damaged area of the sweetpotato. The disease usually begins in the wound
created where roots are broken from the plants during harvest. Diseased
sweetpotatoes turn soft and moist, with stringy flesh. The color of the diseased
tissue may vary among sweetpotato cultivars. The entire root usually rots
completely within days after infection.
 Disease cycle Dispersal: Rhizopus spores are ubiquitous and continually
present in the air around us. Infection: Rhizopus spp. require wounds and necrotic
tissue for infection of sweetpotato storage roots. Disease and symptom
development: Pectolytic and other enzymes produced by Rhizopus quickly cause
host discoloration and liquefy host tissues. It is an efficient saprophyte, surviving
on the dead tissues of its plant hosts or on rotteetpotatoes in fields, in Tufts of the
plant pathogen Rhizopus emerge from openings in a rotting sweetpotato. Fungal
"whiskers," typically darkly colored, fuzzy-looking tufts, are diagnostic for
Rhizopus soft rot disease. Environment and other factors Several variables
influence infection and disease development of Rhizopus soft rot. Effect of wound
periderm: Wound periderm can exclude Rhizopus spp. from the storage roots.
Proper curing conditions create sufficient wound periderm (special tissue formed
around wounds by plants; inhibits entry of microorganisms) to reduce Rhizopus
soft rot significantly. Storage of sweetpotatoes: Sweetpotatoes stored for long
periods of time after harvest are more susceptible to soft rot disease. Integrated
management of Rhizopus rot Contact between infective spores of Rhizopus spp
and sweetpotatoes is almost inevitable because of the ubiquitous and airborne
nature of the pathogens. Rhizopus, a fungal UH-CTAHR Rhizopus Soft Rot of
Sweetpotato PD-68 - Feb. The typical fuzzy tufts of Rhizopus sporangia and
sporangiophores extrude like whiskers through openings and wounds in the
sweetpotato surface. Rhizopus rot can progress rapidl.

Link artikel: https://www.ctahr.hawaii.edu/oc/freepubs/pdf/pd-68.pdf

I. TOPIC

1). Main idea: postharvest disease in sweet potato

2). Topic sentence: rotting under the influence of rhizopus
3). Inter-opinion: Sweet potato decay is caused by the growth of the
Rhizopus fungus, this disease can grow anywhere and cause infection.
usually occurs in the hollow or broken part of the sweet potato.
II. PRONOUN REFERENCE:
4). It is common to see several postharvest diseases of sweet potatoes in the
same batch.
5). It is an efficient saprophyte, surviving on the dead tissues of its plant
hosts or on rotten potatoes in fields, in Tufts of the plant pathogen Rhizopus
emerge from openings in a rotting sweet potato.
6). When the infection is restricted, it is called ring rot or collar rot (it =
infection)
III. VOCABULARY
7). Meaning of word ; phatogens, sweetpotatoes, plant.
8). Uncured sweetpotatoes are more prone to damage than are cured
sweetpotatoes 9uncured)
9). Synonim ; appearance >< physical, production >< result, preserved ><
storability.
IV. PART OF SPEECH
10). The disease usually begins in the wound created where roots are broken
from the plants during harvest (Noun ; broken).
11). Pectolytic and other enzymes produced by Rhizopus quickly cause host
discoloration and liquefy host tissues (quickly : adverb)
12). In Hawai'i, the disease can occur wherever sweetpotatoes are grown or
processed (ajd : grown).