376 >SV>/7 Factors on Disease Resistance 



early February. Of great interest were the results obtained when actively 

 growing indigo plants were cut back. This was followed in all cases by 

 the death of the fine roots and nodules and before new shoots were 

 formed extensive root regeneration was necessary. The formation of new 

 roots during the monsoon was found to be more rapid if there was a 

 break in the rains after cutting back, and to take place much more 

 readily in the case of surface rooted types than if the root-system was 

 deep. The next step in the investigation was to determine whether wilt 

 is actually caused by the gradual destruction of the fine roots and 

 nodules as seemed probable. Wilt was produced experimentally in the 

 following ways: 



(a) By the mutilation of the root-system. One example of wilt 

 produced in this manner may be quoted. An indigo plant was partially 

 cut back on June 21st. 1919. On August 5th, the roots were exposed by 

 the Knapsack sprayer and were found normal and healthy in all respects. 

 Before replacing the soil, the fine roots and nodules on the laterals were 

 removed to the depth of one foot but below this point the soil was not 

 disturbed. Wilt rapidly developed and when the entire root-system was 

 again exposed on August 29th very few active roots were found. 



(b) By deep interculture, during the rains, of indigo sown in lines. 

 Two well-marked cases of this have occurred at Pusa recently. In 1918, 

 Java indigo, sown in double lines with wide spaces between to admit of 

 interculture, speedily lost in vigour and developed much more wilt than 

 the broadcast crop side by side which was not cultivated. In 1919, the 

 experiment was repeated with four types of indigo sown on two different 

 types of soil. The indigo grown in double lines with interculture yielded 

 less crop and developed more wilt than the neighbouring broadcast plots 

 which were not cultivated. The cultivation was found to destroy the 

 lateral roots near the surface on which the plants were dependent at 

 that period of the year. 



(c) By October and November cultivation of old indigo, dependent 

 for its crude sap on superficial roots. After the rains, the only active 

 roots of an old indigo crop are quite close to the surface. If the land is 

 cultivated these are destroyed and wilt develops. Mulching the surface 

 with straw to preserve the moisture and to prevent these roots drying 

 up as the season changes has the reverse effect. 



(d) By cutting back young rapidly growing August-sown plants in 

 October, when the reserve materials in the tap-root are insufficient for 

 root regeneration. Cutting back at this period kills the majority of the 

 plants but a few produce, wilted shoots. 



