under some circumstances, and the non-sporing Gram-positive organism
Corynebacterium sepedonicumcauses a ring rot of potatoes. Table 5.12
lists a range of micro-organisms which may cause spoilage of fresh
vegetables.
The role of plant pathogens in subsequent spoilage post-harvest may
be complex, thusPhytophthora infestanscauses a severe field disease of
the potato plant, frequently causing death of the plant, but it may also
remain dormant within the tubers and either cause a rot of the tubers
during storage, or a new cycle of disease in the next season’s crop.
However, the most frequent agents of spoilage are not the plant path-
ogens themselves but opportunistic micro-organisms which gain access
to plant tissue through wounds, cracks, insect damage or even the lesions
caused by the plant pathogens. All freshly harvested vegetables have a
natural surface flora, including low numbers of pectinolytic bacteria, and
it is becoming increasingly evident that healthy tissue of the intact plant
may also contain very low numbers of viable micro-organisms (end-
ophytic). The onset and rate of spoilage will depend on the interactions
between the physiological changes occurring in the tissues after harvest
and changes in microbial activity. Harvesting itself will produce physio-
logical stress, principally as a result of water loss and wilting, and cut
Table 5.12 Some micro-organisms involved in the spoilage of fresh vegetables
Micro-organism Vegetable Symptom
BACTERIA
Corynebacterium sepedonicum Potato ring rot of tubers
Ralstonia solanacearum Potato soft rot
Pectobacterium carotovorumvar.atrosepticum Potato soft rot
Streptomyces scabies Potato scab
Xanthomonas campestris Brassicas black rot
FUNGI
Botrytis cinerea Many grey mould
Botrytis allii Onions neck rot
Mycocentrospora acerina Carrots liquorice rot
Trichothecium roseum Tomato pink rot
Cucurbits
Fusarium coeruleum Potato dry rot
Aspergillus alliaceus Onion black rot
Garlic
154 Microbiology of Primary Food Commodities