We report below the development of a bioassay employing pollen germination and pollen tube elongation. Five insecticides and five herbicides were tested against 14 inbreds in all possible combinations (Table 1). An additional six inbreds and 12 F1's were also tested against a selection of these agrichemicals. All chemicals were tested at 3 concentrations: the manufacturer's recommended field dose, a tenfold dilution and a one hundredfold dilution of the field dose. 0.1 ml of each concentration was overlaid onto petri plates containing our basal medium which was prepared daily. Control plates received no overlay. All treatments were performed in triplicate. Pollen of known genotype was collected and sieved just prior to application and was delivered to the medium using a No. 2 Camel's hair brush 30 minutes after chemical overlay. Pollen was allowed to germinate for 15 minutes. Five random sample areas from each plate were photographed (Plus X) for a total of 15 samples (approximately 1,000 pollen grains) per treatment. The data are stored on approximately 600 rolls of 35 mm film.
Some preliminary data are presented in Table 2. These results are indicative of the differential responses that we are seeing as we work through the large data pool. Most obvious is the apparent enhancement response of the three inbreds (A158, Oh43, W23) to the insecticide basudin at low concentration and the inhibitory effect of the higher dose.
Table 1. List of materials employed.
|A 158||Mo 17|
|A 619||N 28|
|A 632||Oh 43|
|B 14A||Oh 51A|
|B 73||Va 26|
|H 95||W 22|
|M 14||W 23|
Table 2. Index of pollen (germination) performance
(multiples of 15 observations per entry).
*F.D. = manufacturer's recommended field dose;
Basudin: 1 ml/l
Atrazine: 10 gm/l
In contrast, M14 germinability is not altered by low concentrations of basudin but does show the expected decrease at the higher dose. Germination of W64A pollen was prevented at the concentrations tested. This apparent super-sensivity will be studied further including the possibility that selective male gametocides could be identified initially with this bioassay.
Response to atrazine shows a definite dosage dependency although the inbreds clearly differ in the magnitude of response. The relative insensitivity of A158 appears unique among the inbreds tested.
We will be introducing several innovations in 1980 now that we have identified the range of response that can be anticipated in the system. The active ingredient(s) of these and other chemicals remain to be tested. In addition, we shall attempt pre-treatment of pollen prior to dehiscence. Breeding and selection studies have been initiated to identify the genetic factors in the pollen. Identification of individual plants whose pollen is sensitive or tolerant to an array of chemicals is now possible. Coupled with gamete selection techniques, breeders may be able to incorporate determinable levels of sensitivity into future hybrids.
K. A. Startek and D. B. Walden
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