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| Author(s): |
Nelson Sidnei Massola Júnior
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Piracicaba. |
| Institution: | Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC) |
| Defense date: | 1998-10-30 |
| Advisor: | Ivan Paulo Bedendo |
| Abstract | |
The effect of Corn Stunt and Maize Bushy Stunt Disease on yield, 1000-kernel weight, and percentage of kernels in different sizes was evaluated under field conditions for the susceptible hybrids of com XL-510 and Dina-933e. Fifteen surveys were carried out during the growing seasons of 95/96 and 96/97, in Piracicaba-SP, Jardinópolis-SP, and Jacarezinho-PR. It was also evaluated the effect of time of symptom expression on yield and the relationship between the population of the insect vector and incidence of both diseases. In a second step, it was evaluated the effect of serial inoculations with Spiroplasma kunkelii on some yield components for the hybrid XL-510, under screenhouse conditions, in order to relate time of infection and yield. Finally, the com hybrids AG-951 (resistant) and XL-510 (susceptible) were experimentally inoculated, under greenhouse conditions, with spiroplasma, phytoplasma, and spiroplasma + phytoplasma, in order to verify the multiplication and the effects of the pathogens on these genotypes. In all of these trials, the evolution of the symptoms was evaluated weekly and the yield was quantified at the end of the experiment. All artificial inoculations were performed by infective leafhoppers (Dalbulus maidis) grown in the laboratory. The greater the incidence of the disease in the field, the greater was the losses for all evaluated variables. Yield loss models, fitted on the basis of the final disease incidence in the field, revealed a loss of 0,8% for each increase of 1% in the incidence for both of the hybrids. The same variation in incidence led to reductions on the 1000- kernel weight of 0,8% and 0,4% for the hybrids Dina-933e and XL-510, respectively. The disease also negatively influenced kernel size. Area under disease progress curve (AUDPC) was a good variable for estimating losses. The earlier the symptom expression in the plants, the more severe were the losses for both of the hybrids. It was not observed correlation between disease incidence and D. maidis levels. When corn plants of the hybrid XL-510 were inoculated with S. kunkelii in the screenhouse, the earlier the inoculation time, the more severe was the reduction in grain production and quality. For the interval between days 10 and 38 after crop emergence, for each day that infection was delayed, there was an increase of 0.5% in yield. However, for the period of 38-66 days, there was an increase of 1.5% in yield. Results of the lattest test showed that it was possible to detect spiroplasma and phytoplasma only in the susceptible hybrid, indicating that the resistant one did not multiply the pathogens. Symptom expression and yield reductions were also reported only in the susceptible hybrid. The phytoplasma was more aggressive than the spiroplasma, leading to earlier symptom expression and being responsible for the highest lesses. (AU) | |