THE PHYSIOLOGY OF HOST–PARASITE RELATIONS: IV. THE EFFECT OF MALEIC HYDRAZIDE AND INDOLEACETIC ACID ON THE RUST RESISTANCE OF KHAPLI AND LITTLE CLUB WHEATS

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Abstract
Little Club (rust reaction type 4) and Khapli (rust reaction type 1 with race 15B) wheats were grown in sand culture in 1-qt. crocks or 5-in. pots. Daily applications of maleic hydrazide or indoleacetic acid were started 5 days before (10 days after sowing), on the day of, and 5 days after inoculation with stem rust (Race 15B) and were continued for about three weeks. Maleic hydrazide inhibited growth and, at 5 and 10 mg. per pot, flowering. Type 4 pustules developed on Khapli plants treated with 5 and 10 mg. of maleic hydrazide daily from the 5th day before and from the day of inoculation. Indoleacetic acid (0.5 mg. per pot from the 10th day after sowing) stimulated growth and flowering and slightly increased the resistance of Khapli. Treatments started 5 days after inoculation had no effect on rust development on Khapli, and none of the treatments altered the rust reaction of Little Club. Spores produced on plants treated with maleic hydrazide gave normal rust reactions on untreated plants.The effect of maleic hydrazide on the plants and on rust development was not altered by the simultaneous application of uracil, which reversed the growth inhibition caused by thiouracil. Thiouracil inhibited rust development in the presence of maleic hydrazide.