(baling) is not as effective as open burning, since 

 propane does not achieve the temperatures of open- 

 grass burning (Johnston et al. 1996). 



Seed Cleaning 



Recleaning of seed lots is not very effective in reduc- 

 ing the level of blind seed (de Tempe 1966). Hampton 

 et al. ( 1995) reported that cleaning to a higher seed 

 weight by removing infected seeds improved germina- 

 tion for some seed lots with a high level of infection; 

 but in lots with a low level of blind seed, cleaning 

 simply removed small but viable seed. A relationship 

 between seed weight and germination could not be 

 established. 



Since infected seed are present in screenings, destroy- 

 ing the screenings destroys the inoculum. Destruction 

 of screenings infested with blind seed was advocated 

 by Hardison (1949). 



Methods for Detection and Assessment 



Postharvest Disease Detection and Assessment 



Early methods of blind seed detection involved the 

 direct observation of seed. Gemmell (1940) detected 

 infection by looking for small pinkish spots on 

 dehusked seed under a binocular microscope illumi- 

 nated by direct light on a white background. At 

 Lincoln College in New Zealand, the usual procedure 

 was to place 100 paled seeds under magnification and 

 examine them for infection (Blair 1947). although 

 removing the lemma or palea to examine the caryopsis 

 can be tedious. Sproule and Wright (1966) developed 

 a manually operated apparatus to facilitate the re- 

 moval of lemma and palea. 



Infected seeds generally appear more opaque than 

 healthy seeds. A diaphanoscope was used to differen- 

 tiate infected and healthy seeds based on opacity 

 (Noble 1939, Glasscock 1940. Hyde 1945. Muskett 

 1948). However, opaque seeds can also occur if the 

 seed is weathered before threshing, in which case 

 opacity increases due to pigmentation (Gemmell 1940. 

 Calvert and Muskett 1945, Muskett 1948). 



For estimation of total infection, Hyde (1945), Blair 

 (1947). and Matthews (1980) believed that direct 

 observations were not as reliable as placing seed in 

 water and looking for spores under the microscope. A 

 magnification of 1003 is suitable for examination for 

 conidia of G. temulenta (Calvert and Muskett 1945). 

 The lemma and palea may be removed (Calvert and 



Muskett 1945, Hyde 1945, Sproule and Wright 1966) 

 or left intact (Kolk and Rennie 1978). Kolk and 

 Rennie (1978) soaked seed for 4 hours; Matthews 

 ( 1980) soaked seed for at least 2 hours. 



The number of seeds considered to provide an accu- 

 rate estimate of rate of infection was reported as 100 

 (Calvert and Muskett 1945. Blair 1947. de Tempe 

 1966). 200 (Hyde 1945. Matthews 1980). or 500 

 (Muskett 1948). Matthews ( 1980) referred to the 

 soaking and examination of seed as the "soaking test." 

 Matthews also performed a "'droplet test," in which 

 100 seeds were individually soaked in drops of water 

 on microscope slides for at least 4 hours. The drops 

 were examined at 1003 and classified subjectively as 

 having light, moderate, or heavy spore concentration. 

 However. Matthews did not find a significant correla- 

 tion between the droplet test and ungerminated seed. 



Rose (1945) correlated conidial numbers removed 

 through soaking samples of 100 seeds with germina- 

 tion rate, but high variability in the number of conidia 

 prevented accurate prediction of germination. 

 Hardison (1957) mixed 18 ml of seeds and 18 ml of 

 water in 250-ml flasks, soaked the seeds for 20 

 minutes, then counted conidia in a 0.0063-mnf 

 hemacytometer chamber. The number of conidia per 

 0.0063 mm 3 corresponded to five infection classes 

 ranging from trace to heavy. One to three conidia per 

 0.0063 mm 3 corresponded to a trace infection level, 

 and more than 30 conidia corresponded to a heavy 

 infection. Alderman ( 1999) used a similar seed- 

 washing procedure and established a linear relation- 

 ship between the number of conidia washed from a 

 standardized seed sample and the percentage of 

 infected seed. 



Matthews (1980) described a detection method based 

 on production of apothecia. In this test. 200 seeds 

 were scattered over moist perlite in 14-cm-diameter 

 petri dishes. The dishes were placed in plastic bags 

 and stored at 5 °C for 1 2 weeks. Normal germinated 

 seeds were removed. Dishes were transferred to 20 °C 

 under a 12 hour light/12 hour dark cycle for a further 

 4-5 weeks. Seeds with apothecia were recorded. This 

 procedure estimates the potential inoculum from seed, 

 but since many infected seeds do not produce apoth- 

 ecia, the total number of infected seeds is greatly 

 underestimated. 



The number of seeds infected with viable G. 

 temulenta can be assessed by isolating the pathogen 



20 



