Teliospores are dark reddish to coppery, dull brown or dark brown, some spores typically black/opaque, globose to subglobose, occasionally with a mycelial fragment (apiculus) attached;24-47 µm diameter (about twice that of Tilletia caries);exospore with thick, truncate, compact projections, 1.5-5 µm high, seen in median view. The opacity of the teliospores (Duran and Fischer, 1961) is one factor that differentiates T. indica from T. walkeri that is found on ryegrass (Lolium spp.) (Castlebury and Carris, 1999);other factors include surface ornamentation and size parameters. Sterile cells are intermingled with teliospores in the sori;very variable, globose, subglobose, frequently lacrymiform, yellowish-brown, 10-28 µm wide at their widest point to 48 µm in overall length, with a well developed stalk;walls laminated, up to 7 µm thick.
Primary sporidia usually 64-79 x 1.5-2 µm;secondary sporidia usually 12-13 x 2 µm.
For more information, see Duran and Fischer (1961), Khanna et al. (1968) and Waller and Mordue (1983).
A quarantine procedure for testing seeds of Triticum spp. for T. indica has been described by EPPO (OEPP/ EPPO, 1991b). An EU recommended diagnostic protocol for the detection and identification of T. indica has also been produced (Inman et al., 2003;EPPO, 2007). This protocol has been enhanced for increased sensitivity and specificity by the adoption of more advanced technology (Tan et al., 2010). An updated draft is available from the IPPC website (www.ippc.int).
Crops for seed should be inspected during the growing season, though not while the crop is still green. Field inspection at maturity prior to harvest could be useful, although field symptoms are often very slight and the disease can be difficult to discern even at maturity. Any bunted seeds detected during field inspections should be examined under the microscope for the characteristic teliospores of T. indica. For quarantine purposes, seed should be tested for the presence of the fungus by the washing test (see Seedborne Aspects).
Direct visual observation for Karnal bunt (dry seed inspection) is regarded as insufficient for quarantine purposes because low levels of infection might pass undetected (Agrawal et al., 1986) and even minimal seed infections can substantially contaminate healthy seed lots (Aujla et al., 1988).
Being a non-systemic pathogen, it generally produces not more than four or five bunted kernels in each spike. Detection in the field is very unlikely and the first year of an outbreak usually goes undetected. For instance, detection of T. indica in a seed test sample in Arizona, USA, in 1996 was traced to wheat harvested in 1993 suggesting the pathogen had been present since 1992 (Rust et al., 2005). It had taken at least 4 years for the pathogen to be detected.
Related invasive species
- Tilletia indica
Related Farm Practice
- Feeding
- Effects
T. indica is the fungal pathogen causing Karnal bunt of wheat seeds. Its distribution is mainly limited to northwest India and adjoining countries, North America and South Africa;it is listed as a quarantine pest in Europe, Australia, South America and elsewhere. In North America it was confined to an area in northwest Mexico until 1996, when it was reported from Arizona. Since then, surveys have detected it in a few locations in southwest USA. It has also recently been found in germplasm imported into other continents.
Symptoms depend on climate and are manifested most clearly when cool/warm humid conditions prevail at heading. The fungus causes a reduction in the length of ears as well as in the number of spikelets of bunted ears. Infected plants may be dwarfed. In general, T. indica rarely infects more than a few spikelets per ear and then the affected grains are not swollen. Oblong or ovoid sori, 1-3 mm diameter, develop, containing dusty, brown to black spore masses. These characteristically smell of decaying fish (trimethylamine) as do those of T. tritici, T. foetida and T. contraversa (EPPO/ CABI, 1996). Feeding studies have revealed no adverse health effects, but consumers can begin to taste and smell the fishiness when 3% or more of grain is affected.
The grain is partially destroyed, the attack starting at the hilum and running along the suture, leaving the endosperm intact and covered by the whole or partly ruptured seed coat. In the case of mild infection, only a black point just below the embryo towards the suture is apparent. In advanced attack, tissues along the suture and adjacent endosperm are replaced by spores. The glumes spread apart, exposing the infected grains, and both glumes and grains may fall to the ground.
For more information, see Holton (1949) and Duran and Fischer (1961).
The main host of T. indica is wheat (Triticum spp.) (Aujla et al., 1986, 1987);durum wheat and triticale are less susceptible. Plants are infected within 2-3 weeks of heading.
In inoculation experiments Aegilops spp., Bromus spp., Lolium spp. and Oryzopsis showed varying degrees of susceptibility (Royer and Rytter, 1988).