Convención de Palermo Italia Diciembre de 2000

S ig n i f i c a n t p l ant mor t a l i t y a f te r l at e a n d i n t e n s e cut t i ng h a s b e e n repor ted i n many t r o p i c a l l e g um e s s u c h a s

h um i l i s ( F i sher , 1 9 7 3 ) , C r o t a l a r ia

( Ke s s l e r and S h e l ton , 1 9 8 0 ) . T h i s a l s o occ ur r ed i n t h e pre s e n t expe r i me n t ( L- 5 - 0 ) . H oweve r , inten s e d e f o l i a t i o n provided i t i s done a t a n ear l y s ta g e o f g r ow t h ( E- 5 - 0 ) i s

not l e th a l b u t doe s r e s u l t i n a s i gn i f i ca n t de l ay i n

reg r owth . S im i l a r l y l a t e de f o l i at i o n , provided i t i s l a x ( L- 5 - 4 ) , w i l l n o t - ki l l p l a n t s but w i l l c a u s e an a p pr e c i ab l e d e l a y i n recov e r y . I n c on t r a s t e a r l y l a x d e f o l i a t i on r e s u l t s i n r a p i d r e c ov e r y a l though a s i g n i f i c ant reduc t i on i n y i e l d s t i l l occur s c o mp a r e d with n o de f o l i a t i on . Facto r s wh i c h a r e

known t o a f f e c t the r a t e o f i n i t i a l r e g r owth a f t e r

de f o l i a t i on a r e u s ua l l y r e l a t ed t o :

1 ) The c a rb o h ydrate r e s erve s above a nd be l ow g r o u n d . 2 ) The n um be r of bran che s c a pa b l e o f r eg r owt h .

3 ) The s i z e o f r e s idual l e a f a r e a . 4 ) The numb e r o f g r owing poi n t s .

The impor t a n c e o f c a rbohyd r a te r e s e rve s t o r eg rowth h a s

been recog n i s ed b y many wo r ke r s ( e . g . Yama d a , 1 9 7 5 ;

Hurnph r e y s , 1 9 7 8 b ) . The s e a u t ho r s sugge s ted t h a t r e s e rve

organ i c regrowth

c omp o u nd s are u t i l i z ed dur i ng the e a r l y

and t h a t l a t e r regrowth i s dependent o n

s ta g e s o f l e a f a r e a and pho t o s y n t h e s i s . The rn a r e s e rv e s p l a y i ng t h i s r o l e a r e sugg e s ted t o b e s ug a r s and s t a r c h wh i c h are s to r e d m a i n

the s tern b a s e a n d roo t s ( Yamada , 1 9 7 5 ) . I n t h i s exper iment ,

the TNC ( s u ga r s a nd s tarch ) c on c e n t r a t i o n s w e r e r e l a t

l ow i n both s tubb l e a nd r o o t s i n a l l t r e a tment s , and

showed no d i f f e r e nce between c u t t i n g treatme n t s at a s l a r

stage o f g r owt h . Howeve r , de s p i te t he l ow conc e n t r a t o f

TNC , t h e amoun t s ( ma i n l y s ug a r ) w e r e higher unde r l a x c u t t i ng

than under s ev e r e c u t t i ng o f the p r ima ry b r a n ch e s ( F i g u r e

2 . 1 1 ) s umab l y r e f l ec t ing t h e g r eater s tubb l e y i e l d i n

A s ign i f i c a n t p o s i t ive c o r re l a t i o n w a s a l s o f o u n d b etween r e g rowth y i e l d a nd t h e amount o f TNC i n t h e s tu b b l e ,

s ug g e s t i ng that t h e i n i t i a l r eg r owth a f t e r c ut t i ng w a s

d ep endent upon t h e amount o f the s e r e s e rv e s i n t h e s tu b b l e ( Ta b l e 2 . 6 ) . Th i s h i gh l i gh t s the need t o r e t a i n a g r e a t e r s i z e o f p r imar y b r a n c h a f t e r de f o l i a t i o n and t h e r eb y p r ov i de

a l a r g e r s uppl y o f TNC f o r regrowth - and h e n c e comp e n s a te

f o r the l ow TNC c o n c e n t r a t i on in the s tu bb l e and r o ot s . T h i s

a l s o may exp l a i n why Verano s ty l o wa s abl e t o r ecover u n d e r

l a t e l ax cutting d e s p i te l ack o f r e s idua l p h o t o s y n t h e t i c

t i s sue . Low amo u n t s o f r e s idual TNC und e r s e v e r e c u t t i n g o f t h e pr ima ry branc h , a n d l ow r e s idual l e a f area due t o n a t u r a l

f a l l i ng o f the l owe r l ea ve s , may have accounted f o r t h e

m o r t a l i t y of the s e p l a n t s s oon a f t e r the f i r s t c u t .

T h e number o f b r a nc h e s capa b l e o f regrowth a f t e r c u t t i n g wa s a l s o found t o b e pos i t i v e l y r e l a t e d to r e g r owth i n s om e t r op i c a l l egume s ( Ke s s l e r a n d She l ton , 1 9 8 0 ) . The r e s u l t s o f t h i s s tudy support t h i s f i nd i ng . I n the ea r l y c u t t r e a tme n t

( E- 5 - 4 ) , many b r a n c h e s c a pab l e o f r egrowth h ad a l r e a d y

e l onga ted on the p r imary branche s , whi l e i n the l a t e r c u t

t r e atmen t , t h e b r a n c h e s c apab l e o f r e growth w e r e l ow i n

numbe r immed i a t e l y a f t e r c ut t i ng ( Ta b l e 2 . 2 ) . The r e f o r e ,

s l ow i n i t i a l r e g rowth w a s o b s e rved in t he s e l a t e c u t

t r eatme n t s due t o s l ow bu i l d u p i n br anch produc t i on .

T h e impo r t a n c e o f r e s idua l l e a f area and t h e numb e r o f

g r owing po i n t s a r e s uppo r t e d r e s u l t s obt a w i t h o t h e r

t r o p i c a l l egume s a s i nd i c a t e d by g h c o r r e l a t ion b e t w ee n r e g rowth y i e l d and th e s e parame t e r s ( Gr o f e t a l , 1 9 7 0 ; J o n e s ,

1 9 7 4 ; K e s s l e r and S h e l t on , 1 9 8 0 ; ow and Char s - Edwa r d s ,

1 9 8 0 ) . I t i s a l s o r e l evant that p l a n t s wh i ch we r e c u t a t

l a te r s t ages o f g r owth had l o s t a l l t h e i r l ower l ea v e s

t hrough natu r a l l e a f f a l l and wer e the r e f o r e l a c k i n g i n

phot o s yn t h e t i c t i s s u e . The number o f g r owing po i nt s wa s a l s o

s i gni f i c antly r under t he s e t r e a tmen t s ( E- 5 - 0 a n d L - 5 -

0 ) . W i th the ma r k e d reduction i n TNC amount s , a s d i s c u s s

e a r l i e r , plant s h a d s l ow r e growth and many s oo n d i ed ,

r e s u l t i ng f r om t h e photo s y nthate be ing ins u f f i c i en t t o me e t t h e d emand s f o r r e s p i r a t i o n and g r owth ( Yamada , 1 9 7 5 ) . T h u s

t h e h i g h c or r e l a t i on obta i ned b e tween r eg r ow t h y i e l d a n d s tu b bl e t o r o o t s r a t i o wa s n o t s urpr i s i n g s i n c e d e f o l i a t i o n i s k nown t o a f f e c t r o o t g r owth ( Ke s s l e r and S h e l ton , 1 9 8 0 )

and d e a t h o f r o o t ha s f r equent l y been reported ( Bowe n , 1 9 5 9 ;

Wh i tema n , 1 9 7 0 ; Wh i t eman a nd L u l ham , 1 9 7 0 ) . F u r t h e rmo r e ,

r e s t r i ct ed d e a t h may p l a nt s .

s upp l i e s o f w a t e r and nut r i e n t s b e c a u s e o f a l s o a c count f o r s l ow r e g r owth and d e a t h o f

r o o t t h e

F r o m t h e above r e s u l t s , i t appea r s t h a t r e g r owth o f V e r a n o s t y l o fo l l ow i n g d e f o l i a t i o n i s d e pende n t on t h e s i z e o f p r imary b ranche s a s s o c i a t e d w i t h s ev e r a l r e s i d u a l p l an t c h a r a c t e r i s t i c s v i z . l eve l o f c a rbohyd r a t e r e s e r v e s t h e s tubbl e a n d root s , t h e r e s i d u a l numbe r o f branche s , t h e r e s i dua l numb e r o f growing po i n t s a n d t h e re s i d u a l l e a f a r e a . The c a r bohyd r a t e r e s e r v e s a l though l ow , appea re d t o b e o f s ome impor t a n c e i n th i s r e s p e c t a s d i d the numb e r o f g r ow i n g p o i nt s , wh i l e r e s i du a l l ea f a n d b r a n c h n umb e r w e r e o n l y imp o r t a nt a f t e r t h e f i r s t c u t t i n g . I n c o n t r a s t t h e t o t a l non - s t r u c t u r a l carbohyd r a t e conta ined i n t h e r o o t s wa s o n l y o f v a l u e when t h e p l an t s w e re o l d e r a nd b i g ge r .

The r e s po n s e t o c u t t i ng i n t e rms o f t o t a l p l an t d r y we i g h t wa s a l s o r e l at e d t o t h e above f a c t o r s a s d i s c u s s ed

e a r l r . P l a n t dry we i g h t was not r e d u c e d under 1 t

c ut t i ng . Th i s r e s e w a s ma l y through i n c r e a s e l n s t em , i n f l or e s ce n c e , and t o a l e s s e r extent , i n c r e a s e i n l e a f d r y we i gh t ( F i g u r e 2 . 4 ) . T h e r e s u l t o f th i s d emo n­ s tr a t e d t ha t a l l comp o n e n t s of dry ma t t e r y i e l d c a n