Soft rot is caused by several types of bacteria, but primarily subspecies and pathovars of Erwinia carotovora (now known as Pectobacterium carotovorum) and E. chrysanthemi (now known as Dickeya dadantii). Other bacterial species that cause soft rot include Pseudomonas cichorii, P. marginalis, P. aeruginosa and P. viridiflava.

References:

First Report of Bacterial Stem and Root Rot of Sweetpotato Caused by a Dickeya sp. (Erwinia chrysanthemi) in China- http://dx.doi.org/10.1094/PDIS-06-10-0417

First Report of Bacterial Root Rot of Ginseng Caused by Pseudomonas aeruginosa in China- http://dx.doi.org/10.1094/PDIS-03-14-0276-PDN

Characterization of Pseudomonas viridiflava Causing Alfalfa Root Rot Disease

in Hamedan Province of Iran- http://dx.doi.org/10.4172/2157-7471.1000135

Identification of cold-tolerant Pseudomonas viridiflava and P. marginalis causing severe carrot postharvest bacterial soft rot during refrigerated export from New Zealand- DOI: 10.1046/j.1365-3059.2002.00679.x

Deon, thank you a lot, but these reports have no relation to cereal crops (wheat, barley, rye, oats)

Hey Alex I found these additional articles which relate to root rot of cereal crops. I would think that some pathogenic strains would be host specific and others not. Thus allowing certain pathogens to infect numerous host species. Hope these articles is of value. 

W. E. McKeen, PRELIMINARY STUDIES OF ROOT AND BASAL STALK ROT OF MATURING CORN IN ONTARIO, Canadian Journal of Botany, 1953, 31(1): 132-141, 10.1139/b53-012.

ABSTRACT

In Ontario, basal stalk rot of corn occurs in the autumn and is of major importance, whereas bacterial stalk rot is of no economic significance. The latter disease, which results from stomatal penetration by Erwinia dissolvens, may occur on a few susceptible corn plants in early July during extremely hot humid weather, although ordinarily temperatures are sufficiently low in the province to limit its development. Common basal stalk rot of corn is usually initiated by the spread of organisms from diseased corn roots up into the stalks; rotting may begin also in tunnels produced by corn borers. Diplodia zeae and Gibberella zeae, the two pathogens that are responsible for most of the stalk rotting in the central part of the American corn belt, were of no practical importance during the last two years. Bacteria, Pythium arrhenomanes, and Fusarium moniliforme were commonly found in the necrotic part of the corn stalk. Diseased plants begin to appear in mid-August and daily become more numerous until the first killing frost occurs or the plants become senescent. The leaves suddenly droop and wither, and are dead within four or five days after the first symptoms appear. By this time, the basal part of the stalk is necrotic and at least some of the roots are decayed. Pith tissues are destroyed and the stalk frequently breaks over near the ground level. All stalk rot pathogens finally produce the same syndrome. P. arrhenomanes causes a root necrosis at first which later spreads up into the stalk and, in Ontario, is of major importance in the corn stalk rot disease. Pratylenchus pratensis has been found in corn roots but its importance is unknown.

SABET, K. A. ; SAMRA, A. S. ; HINGORANI, M. K. ; MANSOUR, I. M, Stalk and root rots of Maize in the United Arab Republic, Plant Protection Bulletin, F.A.O. 1961 Vol. 9 No. 7 pp. 121-125 pp.

ABSTRACT

Recently a disease of maize resembling bacterial stalk not caused by Pecto-bacterium cawtovorum [Erwinia carotovora] f. zeae [cf. 40, 358] has become serious in Egypt. In Sept, -Dec. 1960 stalk rots were found to be of 3 types, slow wilt ', wet rot ', and soft rot '. The ' siow wilt ' predominated throughout the growing areas, incidence ranging from 6-25%. Organisms associated with the slow wilt fungus included tRhirdoctonia bataticola. [Macrophemina phasecli], Fusarium monilijorme [Gibberelta fujikuroi], F. app., and Bacterium lath yri; M. phasecli, which induced charcoal stalk rot symptoms, was more frequent than the others. Hybrid vars. were more susceptible than open-pollinated ones. The 1st symptoms of ' slow wilt ' included withering from base to top at flowering or later, leaves turning dull green and finally becoming yellow and dry. Yellow to reddish brown or red streaks appeared on the green stalks; internally they were more pronounced at the nodes. Eventually the lower internodes became hollow and mycelium was visible at the nodes, particularly near soil level. The roots also were stained red at the tips, and any grain which formed was shrunken. The causal pathogen resembles a F., but does not produce typical macroconidia and remains unidentified.

The wet rot condition was prevalent in Minufuja and Kafr EI-Sheikh and is a multiple infection. Symptoms include slow wilt and tissue decay and the disease is considered to be a modification of slow wilt brought about by associated borer attack with accompanying damage by secondary invaders.

Soft rot, observed only once, in Qalyubija Province, is due to infection by B. carotovora f. seas. In nature a characteristic odour is present, but this is not obtained in inoculations with the causal organism. High temp. and 11.11. in May and June 1961 caused this disease to occur.

Charcoal stalk rot appears as a root rot in maize seedlings, but in mature plants the grey, rotted internodes are covered with tiny, black sclerotia, which are also present on the vascular bundles, the sole remains of the internal tissues of affected stalks.

Kernel or ear rot caused by G. fujikuroi has been observed in Egypt, but the pathogen is not considered to play an important part in any of the 3 conditions described, though it is frequently isolated from rotted stalks.

A single plant affected by severe root rot was found in Beni-Suef. A white, fast-growing, cottony mycelium associated with the rot reproduced the disease in inoculations.

Wang, J. S.; Yang, X. Y., Comparative study on the causal bacteria of rice foot rot and maize stalk rot, Acta Phytopathologica Sinica 1991 Vol. 21 No. 3 pp. 181-185.

ABSTRACT

A comparative study of 58 biochemical properties of 18 isolates of rice foot rot bacteria, 17 isolates of the maize stalk rot bacterium, Erwinia chrysanthemi pv. zeae, 6 pathovars of E. chrysanthemi and 2 pathogenic varieties of E. carotovora (subsp. carotovora and subsp. atroseptica), showed that the strains of rice foot rot had phenotypic characters similar to those of E. chrysanthemi pv. zeae. However, differences were observed in blue pigmentation, utilization of malonate and citrate, production of ammonia and catalase activity. The rice root rot isolates had a wider host range and higher virulence. Serological analysis showed that the rice root rot isolates had no common antigens with maize stalk rot isolates.

Deon, many thanks! I expected that it must be mixed infection by bacteria and fungi! The problem is that  Bacterium lath yri = Bacillus lathyri=Erwinia herbicola=Pantoea agglomerans and Erwinia dissolvens=Enterobacter cloacae are very strange plant pathogens with high genetic diversity and large  non-pathogenic part of populations (up to 90%). But, at least I know that I must look for. 

I'll try to ask to Italian colleagues. I wish you a reserch-ful 2015! 

@Deon

@Loredana, Many thanks for help, Happy New Year!