Bacteria - pigeonpea
Contributors to this page: ICRISAT, Patancheru, India (RP Thakur, AG Girish, VP Rao).
Pseudomonas syringae pv. pisi (Sackett) Young et al.
Other scientific name
Importance to CGIAR centers
Severe infection and substantial crop losses have been reported from winter-sown peas in southern France, New Zealand and South Africa (Boelema 1972; Taylor 1972). The disease as such, however, does not appear to be of great economic importance in Europe.
Symptoms usually appear on the stem near the soil as water-soaked and later olive-green to purple-brown spots. The infection extends upwards to the stipules and leaflets, where veins turn brown to black and adjacent tissues become diseased in a fan-like pattern. The interveinal tissues may become water soaked and then yellowish to brown, finally drying out and becoming papery. Lesions on leaflets and pods begin as small, round, oval or irregular dark-green water-soaked spots at first, and later enlarge and coalesce but are sharply defined by the veins. Cream-colored bacterial ooze may be found on the lesion surface that, on drying, gives a glossy appearance. The leaflets later become yellowish and the spots brown and papery. Ripening pods become twisted and dry, lesions on them are sunken and greenish-brown. Lesions on the pod may be limited to a narrow band on the sutures. Infected seeds show a water-soaked spot near the hilum and/or are shrivelled, with a brown-yellow discoloration. Infection often takes place on sepals, spreading to the flowers, and flower buds may be killed before they open.
Pisum sativum var. arvense (peas) is the principal host. Natural infection has also been recorded on Lablab purpureus (hyacinth bean), Lathyrus latifolius (Everlasting-pea or sweet-pea Everlasting), L. odoratus (sweet pea) and Vicia benghalensis (purple vetch).
Bacterial blight is world wide in distribution.
Biology and transmission
Pseudomonas syringae pv. pisi is a motile, gram-negative, non-spore-forming rod, 0.7 ´ 2-3 µm, with one to five polar flagella. Disease has been observed to develop more readily on soils with high moisture content. Infections can occur through contact of diseased and healthy foliage and insects may have a role in transmission. The bacterium can survive on or within seeds for at least 10 months (Skoric 1927) and for several months on diseased plant debris in the field (Harris 1964).
Detection/indexing methods at ICRISAT
- Detection of the pathogen in seeds is usually performed by soaking ground pea seeds in buffer at low temperature (4°C) for 4-16 h and subsequent isolation from the (centrifuged) soaking solution. For isolation from diseased tissues and seeds, King's medium B can be used, with supplement of boric acid, cephalexin and cycloheximide if necessary (Mohan and Schaad 1987).
- Not known since it is not detected at ICRISAT.
Procedures followed in case of positive test at ICRISAT
- Incineration of the infected crop and rejection of the seed samples.
EPPO (OEPP/EPPO 1990) recommends that pea seeds should come from a field or area free from P. syringae pv. pisi, or else that the seed crop should have been inspected. However, seed-testing techniques are now available to detect the bacteria.
References and further reading
Boelema BH. 1972. Bacterial blight (Pseudomonas pisi Sackett) of peas in South Africa, with special reference to frost as a predisposing factor. Mededelingen Landbouwhogeschool Wageningen 72: 1-87.
Harris DE. 1964. Bacterial blight of peas. Journal of Agriculture, Victoria Department of Agriculture 62: 276-280.
Mohan SK, Schaad NW. 1987. Semiselective agar medium for isolating Pseudomonas syringae pv. syringae and pv. phaseolicola from bean seed. Phytopathology 77: 1390-1395.
OEPP/EPPO. 1990. Specific quarantine requirements. EPPO Technical Documents No. 1008.
Skoric V. 1927. Bacterial blight of peas; overwintering, dissemination and pathological histology. Phytopathology 17: 611-628.
Taylor JD. 1972. Races of Pseudomonas pisi and sources of resistance in field and garden peas. New Zealand Journal of Agricultural Research 15: 441- 447.