Plant and Soil 47, 245-248 (1977) Ms. 2682

S H O R T C O M M U N I C A T I O N

Survival and retention of infectivity of bacterial stalk rot pathogen of maize and its perpetuation on varied

cropping pattern

Summary The sterilized environment prompted the maize stalk rot pathogen Erwin ia

carotovora f. sp. zeae Sabet to retain its infectivity for a longer period than the unsterilized one. The survival as well as infectivity potency of the pathogen present in the soil having naturally-infested or artificially-inoculated host plant as debris was superior to tha t in the soil or even the soil containing maize stalk tissue.

'Maize-potato-maize' cropping pat tern effected a considerable increase in the disease incidence due to maintainance of continuity of life of the pathogen in the intervening potato crop.

Introduction

Plant pathogenic bacteria survive in the soil 7 as well as in the host tissue debris 1 10 for fairly long periods. Yet the perpetuation of the disease gets influenced by the preceding crop s.

However the twin studies enumerated below would present the mode of survival of Erwin ia carotovora f. sp. zeae and also the impact of varied crop- ping pat tern on the extent of disease incidence.

Materials and methods

Infect ivi ty potential of maize stalk rot pathogen Erwin ia carotovora f. sp. zeae Sabet was examined under four conditions, namely, in the soil alone (A), soil containing decomposable maize stalk tissue (B), soil debris having natu- rally infected maize plant (C) and soil debris having artificially inoculated plants (D). The assessment of bacterial population through dilution plate method 4 was, however, done for the first two parameters only. Four replicates of ten pots each were maintained under natural field conditions. Experiments were carried out each month for two consecutive years.

To achieve the first two conditions 250 ml of the thoroughly rocked young broth culture (48 h old) of the pathogen was mixed separately with sterilized and unsterilized soil (A) and also with sterilized and unsterilized soil having heal thy maize stalk tissue (13). These were kept in 6" earthen pots. Controls were maintained.

246 SHORT COMMUNICATION

The presence a n d i d e n t i t y of t h e p a t h o g e n i c fo rm was con f i rmed each m o n t h b y p l a t i n g t h e t r e a t m e n t on P C V (Pec t in -c rys ta l -v io le t ) m e d i u m 2.

Fo r o b t a i n i n g soil debr i s t h e n a t u r a l l y in fec ted a n d ar t i f ic ia l ly inocu la t ed p l a n t s were c h o p p e d s e p a r a t e l y in to v e r y sma l l pieces a n d m i x e d s e p a r a t e l y w i t h s ter i l ized a n d uns te r i l i zed soil. T h e y were t h e n b u r i e d u p t o a d e p t h of 6" in s ter i l ized e a r t h e n pots . Cont ro l s were m a i n t a i n e d u n d e r open field condi- t ions concu r r en t l y .

Fo r a n ana lys i s of t h e i n f e c t i v i t y p o t e n t i a l a sma l l a m o u n t of soil or of soil w i t h debr is was r e m o v e d f rom t h e bu r i ed soil. I t was c ru s h ed in s ter i le d is t i l led w a t e r a n d a l lowed to s t a n d for a few minu t e s . Th i s suspens ion was t h e n i n o c u l a t e d i n to t h e 21-day old maize p l a n t s ra i sed in s ter i l ized soil k e p t in 6" p las t i c pots , E a c h p o t c o n t a i n e d 5 p l an t s . T h e p l a n t s were k e p t in c h a m b e r s h a v i n g a t e m p e r a t u r e of 35°C, 7 0 % r.h. a n d 12 h of pho tope r iod . 48 h a f t e r i nocu la t i on t h e resu l t s were recorded .

The p e r p e t u a t i o n p a t t e r n of t h e disease was s u r v e y e d for t e n d i f fe ren t c r o p p i n g t y p e s (Table 2). Th i s was done for 3 consecu t ive years a n d t h e p e r c e n t a g e of inc idence of disease was r ecorded ~.

TABLE 1

The survival of stalk rot pathogen in soil (A), soil containing maize stalk tissue (B), soil debris having naturally infected maize plant (C) and soil debris having artificially inoculated maize plant (D) expressed as population of the pathogen in millions/g of soil

(i) and pathogenecity potency on 21 day old maize plant (ii)

Months

Sterilized Unsterilized

(A) (B) (C) (D) (A) (B) (C) (D)

(i) (ii) (i) (ii) (ii) (ii) (i) (ii) (i) (ii) (ii) (ii)

First year Nov. 6.30 Dec. 8.50 Jan. 0.95 Feb. 0.02 March April May June July

Second year Nov. 8.40

Dec. 9.58 Jan. 0.98 Feb. 0,04 March April May June July

+ 7.68 + + + 22.30 + 20.86 + + + + 9.85 + + + 8.50 + 6.54 + + + + 4.25 + + + 0.05 + 0.54 + + + + 1.20 + + + -- -- 0.06 + + +

0 . 8 5 + + + . . . . + + 0.02 + + + . . . . + + __ __ + + . . . . + +

__ __ + + . . . . + +

__ __ + + . . . . + +

-5 9.65 -5 -5 -5 25.50 + 22.80 -5 -5 -5

+ 12.10 + -5 + 9.50 + 8.45 -5 -5 + -5 6.25 + + + 0.04 -5 0.20 -5 ~- -5

+ 4.12 + -5 + -- -- 0.04 -5 -5 -5 1.65 + -5 + . . . . + +

0.07 + -5 -5 . . . . + + __ __ + + . . . . + +

__ __ + + . . . . + +

__ __ + -5 . . . . + +

SHORT COMMUNICATION

TABLE 2

The percentage of disease incidence of stalk rot of maize in different crop rotational pattern

247

Cropping patterns Incidence of stalk rot (%)

1st year 2nd year 3rd year

1. Maize-potato-maize 30 55 75 2. Maize-wheat-maize 25 20 20 3. Rice-potato-maize 15 20 30 4. Soybean-potato-maize 15 20 35 5. Maize-pea-maize 30 20 10 6. Sorghum-wheat-maize 25 15 15 7. Soyabean-wheat-maize 20 15 10 8. Rice-wheat-maize 20 10 10 9. Sorghum-potato-maize 20 25 40

10. Maize-Lahi-pot ato-maize 30 50 70

Results

T a b l e 1 includes t h e mode of s u r v i v a l a n d r e t e n t i o n of i n f ec t i v i t y of ma ize s t a l k r o t p a t h o g e n a n d T a b l e 2 p re sen t s p e r p e t u a t i o n p a t t e r n on d i f fe ren t c rop r o t a t i o n a l types .

Discussion

In i t i a l l y t h e a m o u n t of E. carotovora f. sp. zeae was h igher in t h e uns te r i l i zed soil t h a n in t h e s ter i l ized one. Th i s was t r u e also of t h e soil c o n t a i n i n g h e a l t h y ma ize t issue. T h e i r n u m b e r , however , dec l ined more r ap id ly u n d e r uns te r i l i zed cond i t ions t h a n u n d e r s ter i l ized cond i t ions (Table 1). Now t h i s suggests a v igorous s a p r o p h y t i c compe t i t i on , w h i c h is c o r r o b o r a t e d b y t h e fac t t h a t t h e r e t e n t i o n of i n f ec t i v i t y of t h i s p a t h o g e n was for a sti l l s h o r t e r pe r iod u n d e r uns te r i l i zed condi t ions . Th i s was app l icab le to E. carotovora 8, Xanthomonas musicola 5, Pseudornonas lapsa 7, a n d X . oryzae 9.

A s e q u e n t i a l b e h a v i o r a l p a t t e r n of m o d e of su rv iva l was d iscern ib le u n d e r four ecological ly v a r y i n g s i tua t ions . I n t h e soil a lone t h e p a t h o g e n E. caroto- vora f. sp. zeae cou ld n o t su rv ive a n d r e t a i n i ts i n f ec t i v i t y b u t for a few m o n t h s . Compara t i ve ly , t h e d eco mp o s ab l e maize s t a lk t i ssue p r o v i d e d a l a rger a n d b e t t e r n u t r i t i v e a l t e r n a t i v e ; b u t could p u s h t h e s u r v i v a l a n d r e t e n - t i o n of i n f ec t i v i t y for on ly a few m o n t h s more . This , inc iden ta l ly , c o n f o r m e d to t h e o b s e r v a t i o n s m a d e for P. lapsa 7 a n d P. solanacearum 8.

T h e i n f ec t i v i t y p o t e n c y of t h e s u r v i v i n g p a t h o g e n was t h e h i g h es t (i.e, for 9 m o n t h s ) in t h e soil h a v i n g debr is of in fec ted a n d ar t i f ic ia l ly i nocu la t ed maize p l a n t s (Table I). Th i s could be so because t h e t i ssue debr is was sole r e se rvo i r for p r o t e c t i o n a n d n u t r i t i o n of t h e p a t h o g e n i c b a c t e r i a E. carotovora f. sp. zeae. A n u t r i t i o n a l c o n t i n u u m was m a i n t a i n e d b e t w e e n t h e s u r v i v i n g p a t h o g e n a n d p l a n t m a t e r i a l debr is . Th i s h a s b e e n e m p h a s i z e d a l r eady for a n g u l a r leaf spo t of c o t t o n 1 a n d a n g u l a r leaf spo t of c u c u m b e r 10.

248 SHORT COMMUNICATION

W i t h p o t a t o as an i n t e r v e n i n g c rop b e t w e e n maize crops (Table 2) t h e inc idence of t h e disease was t h e h ighes t . T h e p o t a t o t h u s ac t ed as a br idge c rop ef fec t ing t he c o n t i n u e d presence of t h e p a t h o g e n .

Acknowledgernents

The a u t h o r s are i n d e b t e d to Professor Y. L. N e n e , H e a d of t h e d e p a r t m e n t of P l a n t P a t h o l o g y , G.B. P a n t U n i v e r s i t y of Agr i cu l tu re a n d Technology, P a n t n a g a r for t h e facil i t ies m a d e ava i l ab le to t h e m .

~¢[AHENDRA PRASAD a n d SATISH KUMAR SINHA

Department of Botany, Ranchi University, Ranchi-834008, India

Received 13 November 1974. Revised September 1976

Re/erences

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5, 333 ~ 1971). 4 P r a s a d , M., Zentralbl. Bakteriol. II 122, 341 (1968). 5 R a n g a s w a m i , G. and R a n g r a j a n , M., Indian Phytopathol. 19, 294 (1966). 6 R a n g a s w a m i , G. and T h i r u n a v u k a r a s a s u , V., Indian Phytopathol. 17, 202

(1964). 7 R a n g r a j a n , M. and C h a k r a v a r t i , B. P., Plant and Soil 33, 140 (1970). 8 R i c h a r d s o n , J. K., Can. J. Res. 20, 241 (1942). 9 S ingh , R. N., Indian Phytopathol. 24, 153 (1971).

10 v a n Gundy , S. D. and Walke r , J. C., Plant Dis. Rep. 41, 140 (1957).