Maturity Effects on Fruit Characteristics, Germination, and Emergence of Sugarbeet 1
F. W. SNYDER 2
Maturity Effects on Fruit Characteristics,
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a n d t h e n a i r - d r i e d t o e q u i l i b r i u m . All s a m p l e s w e r e w e i g h e d a n d p l a c e d o n u n i f o r m l y m o i s t e n e d d o u b l e b l o t t e r s i n a g e r m i n a t o r . A f t e r 4 8 h , t h e s a m p l e s w e r e r e m o v e d a n d r a p i d l y w e i g h e d . P e r c e n t a g e s w e r e c a l c u l a t e d as follows:
% water absorption = Wet wt — Air-dry wt x 100
r A i r - d r y wt
Experiment 2: S u g a r b e e t m o t h e r r o o t s of five m o n o g e r m c u l t i v a r s w e r e h a r v e s t e d a t East L a n s i n g , M i c h i g a n i n N o v e m b e r 1970. T h e y w e r e s t o r e d at a b o u t 4°C u n t i l t h e y w e r e p l a n t e d in soil ( 2 5 . 4 - c m pots) i n t h e g r e e n h o u s e i n J a n u a r y 1971 for s e e d p r o d u c t i o n . F r u i t i n g b r a n c h e s f r o m 1 1 p l a n t s w e r e h a r v e s t e d a t 4 0 , 5 0 , 6 0 , a n d 7 0 d a y s after f i r s t b l o o m a n d f r o m 1 0 p l a n t s a t 4 0 , 4 5 , 5 0 , 5 5 , 6 0 , 6 5 , 7 0 , a n d 7 5 d a y s . F r e s h w e i g h t s o f t h e w h o l e fruits w e r e o b t a i n e d a t e a c h h a r - vest t o d e t e r m i n e m o i s t u r e c o n t e n t . T h e fruits w e r e a i r - d r i e d i n t h e l a b o r a t o r y .
Part 1: F r u i t s f r o m 11 p l a n t s w e r e s e p a r a t e d by p l a n t a n d by t h e f o u r t i m e s of h a r v e s t (11 x 4 = 44 lots). F r u i t s f r o m e a c h lot w e r e d i v i d e d i n t o six s a m p l e s o f 4 0 fruits e a c h (five s a m p l e s h a d lesser n u m - b e r s ) . T w o s a m p l e s w e r e u n t r e a t e d ; two w e r e s o a k e d i n 5 0 m l t a p w a t e r for 2 h, quickly r i n s e d , a n d a i r - d r i e d to e q u i l i b r i u m ; two w e r e h a n d - p r o c e s s e d t o r e m o v e t h e c o r k . E a c h s a m p l e was w e i g h e d a n d p l a c e d o n a d o u b l e l a y e r o f m o i s t e n e d b l o t t e r s i n a n u n c o v e r e d P e t r i dish in a g e r m i n a t o r at a b o u t 2 1°C for 40 h. W a t e r was a d d e d twice d u r i n g t h e 4 0 - h p e r i o d t o r e p l e n i s h t h a t lost b y e v a p o r a t i o n a n d ab- s o r p t i o n b y t h e fruits. A f t e r t h e a b s o r p t i o n p e r i o d , s a m p l e s w e r e w e i g h e d a n d t h e n r e t u r n e d t o t h e g e r m i n a t o r for 10-day g e r m i n a t i o n d a t a . W a t e r a b s o r p t i o n was c a l c u l a t e d as in E x p e r i m e n t 1. P e r c e n t a g e w e i g h t losses in w a t e r - s o l u b l e s u b s t a n c e s a n d in r e m o v a l of c o r k y m a t e r i a l w e r e c a l c u l a t e d b y w e i g h i n g t h e fruit s a m p l e s b e f o r e s o a k i n g a n d p r o c e s s i n g a n d a g a i n a t a i r - d r i e d e q u i l i b r i u m a f t e r t r e a t m e n t .
Part 2: F r u i t s f r o m 10 p l a n t s (five cultivars), s e p a r a t e d by p l a n t a n d b y t i m e o f h a r v e s t , w e r e h a n d - p r o c e s s e d . F o r e a c h p l a n t a n d e a c h t i m e o f h a r v e s t , 8 0 fruits w e r e u s e d for b l o t t e r g e r m i n a t i o n a n d 9 6 for s a n d e m e r g e n c e . T h e fruits w e r e p l a n t e d i n plastic b o x e s a t a d e p t h o f 3.8 c m i n f i n e q u a r t z s a n d a t 4 % m o i s t u r e . A f t e r 1 2 d a y s a t a b o u t 70°F, all o f t h e fruits w e r e a c c o u n t e d for b y c a t e g o r i e s , i.e., s e e d l i n g s e m e r g e d , g e r m i n a t e d i n s a n d b u t n o t e m e r g e d , n o t g e r m i n a t e d , a n d j u d g e d t o b e n o n v i a b l e . All g e r m i n a t i o n a n d e m e r g e n c e p e r c e n t a g e s
w e r e c a l c u l a t e d o n t h e basis o f t h e n u m b e r o f viable s e e d s . R e s u l t s
Water absorption by fruits
Experiment 1: I m m a t u r e fruits of this c u l t i v a r a b s o r b e d m u c h m o r e w a t e r t h a n m a t u r e fruits ( T a b l e 1). N e i t h e r p l a n t s o u r c e n o r
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fruit size significantly affected water absorption for a given maturity.
Soaking and processing fruits substantially decreased the quantity of absorbed water, particularly in immature fruits.
Table 1.—Effect of maturity, processing, and soaking on water absorption by air-dried sugarbeet fruits in 48 h.
aA i r - d r y basis.
Experiment 2, Part 1: As sugarbeet fruits matured, they usually
absorbed progressively less water (Fig. 1). Water absorption after the soaking treatment did not follow this pattern consistently. Two culti- vars (five plants) averaged 115% water absorbed at 40 days after first bloom and increased to 138% absorbed at 60 days. The soak treatment increased the quantity of water absorbed by fruits in 14% of the samples by at least 10% over that absorbed by untreated fruits. Thus for some cultivars, the soak treatment appears to induce changes in the fruits at specific stages of maturity that enhance rather than sup- press water absorption.
Figure 1.—Effect of maturity and treatments (U—untreated, S—soaked, P—processed) on water absorption by air-dried sugarbeet fruits (air dry basis). Means and standard deviations for 11 plants.
aNS = not significant; * significant at 5% and ** at 1%; dt = 9.
Table 4.—Correlation between fruit moisture at harvest and germination of seeds of sugarbeet plants.
aNS = not significant; * significant at 5% and ** at 1%.
Fruit-weight losses by processing and soaking
As maturity progressed, the fruit-weight losses by processing increased, but weight losses by soaking decreased (Fig. 2). At maturity, weight loss by hand-processing approximated a quarter of the fruit weight, whereas losses by soaking were lowest. Weight losses among the 11 plants varied most at 40 to 50 days after first bloom and least at maturity.
For the 40-, 50-, and 60-day harvests, losses in weight by soaking correlated significantly with fruit moisture (r = 0.79** to 0.87**), but losses in weight by processing correlated with fruit moisture only for the 40- and 50-day harvests (r = - 0 . 9 4 * * and -0.80**, respectively).
aNS = not significant; * significant at 5% and ** at 1%; df = 9.
Table 3.—Correlation between water absorption by air-dried sugarbeet fruits and germination of the seeds from 11 plants.
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Water absorption by the processed fruits of the 11 plants was correlated with fruit moisture at harvest (r = 0.74** to 0.91**) (Table 2). Germination percentages correlated inversely with water absorp- tion, and significantly for processed fruits at 40, 50, and 60 days after first bloom (Table 3). Germination also correlated inversely with fruit moisture at harvest (Table 4).
Table 2.—Correlation coefficients between fruit moisture at harvest versus subsequent water absorption by air-dried sugarbeet fruits from 11 plants.
Figure 2.—Relation of weight loss in processing and soaking to time of harvest of sugarbeet fruits. Process, Soak treatments. For the consecutive harvests, mean fruit moisture percentages were 206±35, 144±58, 75±58, and 37±27.
Germination response by time of harvest
T h e g e r m i n a t i o n p e r c e n t a g e s for t h e f i v e cultivars ( T a b l e 5 ) i n d i c a t e t h a t at full m a t u r i t y it is very difficult to select t h e cultivars with t h e m o s t d e s i r a b l e g e r m i n a t i o n . I f w e e x a m i n e t h e d a t a u n d e r c o l u m n s " P " in Table 5, f o u r of five cultivars g e r m i n a t e d in excess of 9 0 % w h e n h a r v e s t e d a t 6 0 days a f t e r f i r s t b l o o m , b u t a t 5 0 days o n l y t h r e e , a n d a t 4 0 d a y s only o n e .
Table 5.—Relation of germination percentage to time of harvest and treatment of sugarbeet fruits.
@U is untreated; S is soaked, see text; P is processed.
Germination response to fruit treatment
Cultivars differed in germination patterns and in their response to the fruit treatments. These differences were more striking with progressively greater immaturity (Table 5). Individuals within a culti- var tended to follow a pattern for a given set of treatments; thus data could be averaged to indicate cultivar performance.
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Relation of fruit moisture at harvest and germination in cultivars T h e m e a n s of cultivars 1 a n d 4 differ significantly, b o t h for fruit m o i s t u r e a t h a r v e s t a n d for g e r m i n a t i o n p e r c e n t a g e s a t 4 0 days ( T a b l e 6). T h e s t a n d a r d d e v i a t i o n s o f t h e c u l t i v a r s s u g g e s t t h a t c e r t a i n o n e s m a y h a v e m u c h less variation i n fruit m o i s t u r e a n d g e r m i n a t i o n p e r - f o r m a n c e t h a n o t h e r s . U s i n g t h e m e a n values for fruit m o i s t u r e a n d g e r m i n a t i o n in T a b l e 6, t h e c o r r e l a t i o n coefficient b e t w e e n t h e s e at.
4 0 d a y s after f i r s t b l o o m was 0 . 8 6 ; b u t with t h r e e d e g r e e s o f f r e e d o m , 0.88 i s r e q u i r e d for significance a t t h e 5 % level. T h e c o r r e l a t i o n was less at 50 d a y s a f t e r first b l o o m .
Table 6.—Relation of fruit moisture at harvest to germination percentage for five cultivars of sugarbeet.
Relation of blotter germination to sand emergence on given days after first bloom O n t h e basis o f t h e g e r m i n a t i o n d a t a , seeds o f t h e s e p l a n t s h a d a t t a i n e d physiological m a t u r i t y 4 0 t o 5 5 d a y s a f t e r first b l o o m (Fig. 3).
H o w e v e r , o n t h e basis o f s a n d - e m e r g e n c e d a t a , c o m p l e t e physiological m a t u r i t y was n o t a t t a i n e d for an a d d i t i o n a l 5 to 15 d a y s .
T h e s a n d - e m e r g e n c e test r e v e a l e d t h a t c e r t a i n s e e d l o t s e m e r g e d r a t h e r p o o r l y a n d t h a t e m e r g e n c e was p o o r i n fully m a t u r e d s e e d (Fig. 3). S e e d s o f two p l a n t s e m e r g e d only 7 0 % , r e g a r d l e s s o f w h e n t h e y w e r e h a r v e s t e d a f t e r first b l o o m .
D i s c u s s i o n
T h e c o r r e l a t i o n s t u d i e s i n d i c a t e t h a t t h e a m o u n t o f w a t e r a b - s o r b e d by s u g a r b e e t fruits is closely r e l a t e d to fruit m o i s t u r e at h a r v e s t a n d t h e d e g r e e o f m a t u r i t y , a n d t h e s e , i n t u r n , i n f l u e n c e g e r m i n a t i o n . Also, p r o c e s s e d fruits a p p a r e n t l y h a v e m o r e p r e d i c t a b l e r e l a t i o n s h i p s b e t w e e n fruit m o i s t u r e a t h a r v e s t , s u b s e q u e n t w a t e r a b s o r p t i o n , a n d seed g e r m i n a t i o n t h a n e i t h e r u n t r e a t e d o r s o a k e d fruits. Since g r o w e r s p l a n t u n s o a k e d , p r o c e s s e d s e e d s i n t h e f i e l d , s e e d s t r e a t e d similarly s h o u l d p r o v i d e m o r e reliable e s t i m a t e s o f g e r m i n a t i o n p o t e n t i a l , a s well a s e l i m i n a t e t h e t i m e - c o n s u m i n g s o a k i n g p r o c e d u r e .
T h e e v i d e n c e s e e m s clear t h a t a t full m a t u r i t y , s u g a r b e e t fruits a n d s e e d s (for cultivars or i n d i v i d u a l p l a n t s ) d i f f e r m u c h less in a g i v e n c h a r a c t e r i s t i c t h a n a t t h e m o r e i m m a t u r e s t a g e s . T h u s , f u r t h e r s t u d i e s
Figure 3.—Effect of maturity on germination and emergence of seed- lings from 10 sugarbeet plants. At full maturity, a sizable range occurs in percentage of emergence, but not in percentage germination.
t o d e t e r m i n e t h e significant fruit a n d seed characteristics t h a t influence g e r m i n a t i o n p e r f o r m a n c e s h o u l d b e m a d e o n i m m a t u r e fruits a n d seeds, p r o b a b l y a r o u n d 4 0 days after f i r s t b l o o m . A s p r e s e n t l y c o n - ceived, a n y system o f t e s t i n g for a n d isolating s u p e r i o r g e r m i n a t i o n p e r f o r m a n c e w o u l d r e q u i r e t h e following: 1. D a t e of first b l o o m for e a c h p l a n t , 2 . d e t e r m i n a t i o n o f t i m e interval b e t w e e n first b l o o m a n d t h e s e e d ' s physiological m a t u r i t y , a n d 3. fruit m o i s t u r e at h a r v e s t c o i n c i d i n g with physiological m a t u r i t y . A l t h o u g h a single, fixed t i m e o f h a r v e s t w o u l d m i n i m i z e t h e t i m e r e q u i r e d t o harvest a n d t h e n u m - b e r of s a m p l e s for g e r m i n a t i o n , two h a r v e s t s at a b o u t a 10-day i n t e r v a l w o u l d p r o b a b l y b e b e t t e r t o isolate t h e s u p e r i o r plants.
T h e t i m e interval b e t w e e n first b l o o m a n d h a r v e s t is r e q u i r e d as a r e f e r e n c e for fruit m o i s t u r e , b e c a u s e t h e m e a n fruit m o i s t u r e o f d i f f e r e n t cultivars m a y vary m a r k e d l y at a given i n t e r v a l after first b l o o m ( T a b l e 6), as well as w h e n t h e seed first b e c o m e physiologically m a t u r e (1). D a t a ( T a b l e 6) s u g g e s t t h a t early loss of fruit m o i s t u r e in h e a l t h y p l a n t s m a y b e r e l a t e d t o early seed m a t u r i t y .
T e K r o n y (3) r e p o r t e d t h a t i n d i v i d u a l f l o w e r s p r o d u c e d s e e d s t h a t g e r m i n a t e d 20 days after a n t h e s i s , a n d t h a t all seed in t h e field was physiologically m a t u r e a b o u t 4 5 days a f t e r p e a k anthesis. P e a k a n t h e s i s w o u l d o c c u r 10 to 15 days after first b l o o m ; t h u s t h e s e results g e n e r a l l y
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c o n f i r m T e K r o n y ' s c o n c l u s i o n s . N o t e , h o w e v e r , t h a t this a p p l i e s only t o b l o t t e r g e r m i n a t i o n . T h e s a n d - e m e r g e n c e r e s u l t s reveal t h a t t r u e physiological m a t u r i t y i s s o m e w h a t l a t e r t h a n i n d i c a t e d b y t h e g e r - m i n a t i o n test. T h u s , h a r v e s t of c o m m e r c i a l s e e d for field p l a n t i n g s h o u l d b e d e l a y e d l o n g e r t h a n w o u l d b e c o n s i d e r e d a d e q u a t e o n t h e basis of p e r f o r m a n c e in t h e b l o t t e r - g e r m i n a t i o n test.
Since t h e g e r m i n a t i o n test failed t o d e t e c t s e e d l o t s t h a t w o u l d e m e r g e p o o r l y in t h e s a n d - e m e r g e n c e test, it s h o u l d n o t be u s e d as a selection t e c h n i q u e t o o b t a i n c o m m e r c i a l c u l t i v a r s w i t h i m p r o v e d e m e r g e n c e .
I n m y first r e p o r t o n t h e effect o f m a t u r i t y , I s t r e s s e d diversity o f t h e p l a n t s within cultivars (1). Analysis o f a d d i t i o n a l d a t a c o n f i r m s t h e diversity, since t h e m e a n v a l u e s for cultivars m a y d i f f e r a p p r e c i - ably. I n a d d i t i o n , t h e d a t a for t h e i n d i v i d u a l p l a n t s within c e r t a i n cul- tivars t e n d t o g r o u p r a t h e r closely a r o u n d t h e m e a n , e.g., c u l t i v a r 1 , 4 0 d a y s after first b l o o m ( T a b l e 6). T h i s g r o u p i n g t e n d e n c y s u g g e s t s t h a t t h e s e d i f f e r e n c e s m i g h t b e u n d e r g e n e t i c c o n t r o l a n d , i f this i s t r u e , m a y b e s u s c e p t i b l e t o selection p r e s s u r e .
F r o m o b s e r v a t i o n s t h u s f a r , t h e f o l l o w i n g d e d u c t i o n s a n d h y p o t h e s e s a r e s u g g e s t e d : 1 . W a t e r a b s o r p t i o n b y t h e s u g a r b e c t fruit i s i n f l u e n c e d b y o n e o r m o r e h y d r o p h i l i c c o m p o u n d ( s ) (J. M . S e b e s o n , Sr., now d e c e a s e d , u n p u b l i s h e d d a t a ) . 2 . B a s e d o n t h e effect o f p r o c e s - s i n g o n w a t e r a b s o r p t i o n (Fig. 1), m u c h o f t h e c o m p o u n d ( s ) i s i n t h e c o r k y m a t e r i a l . 3 . S i n c e w a t e r a b s o r p t i o n g e n e r a l l y d e c r e a s e s a s m a t u r i t y a p p r o a c h e s a n d i s least w h e n fruits a r e c o m p l e t e l y a i r - d r i e d while a t t a c h e d t o t h e p l a n t , t h e q u a n t i t y o f t h e active c o m p o u n d ( s ) s h o u l d d e c r e a s e in a similar m a n n e r . 4. As m a t u r i t y p r o g r e s s e s in fruits a t t a c h e d t o t h e p l a n t , a t least s o m e o f t h e c o m p o u n d ( s ) m u s t b e a l t e r e d to a n o n - h y d r o p h i l i c e n t i t y . 5. S o a k i n g fruits of c e r t a i n p l a n t s ( E x p e r i m e n t 2 ) d e c r e a s e d t h e effect o f t h e h y d r o p h i l i c c o m p o u n d ( s ) , while i n o t h e r s s o a k i n g e n h a n c e d t h e effect; t h u s a n u m b e r o f m o d e s o f action may o c c u r , s u c h a s diffusion o f t h e c o m p o u n d ( s ) f r o m t h e fruit i n t o t h e w a t e r , a n d possibly h y d r o l y s i s t o e i t h e r m o r e o r less active e n t i t i e s . T h e c o m p l e x i t y o f t h e effects i s a p p a r e n t .
S u m m a r y
D r i e d i m m a t u r e s u g a r b e e t fruits g r o w n i n O r e g o n a b s o r b e d significantly m o r e w a t e r t h a n m a t u r e fruits.
S u g a r b e e t fruits f r o m 2 1 p l a n t s (five cultivars) g r o w n i n t h e g r e e n - h o u s e w e r e h a r v e s t e d p e r i o d i c a l l y , b e g i n n i n g 4 0 d a y s a f t e r first b l o o m , a n d a i r - d r i e d i n t h e l a b o r a t o r y . U n t r e a t e d a n d h a n d - p r o c e s s e d fruits h a r v e s t e d a t 4 0 days a b s o r b e d significantly m o r e w a t e r t h a n fruits h a r v e s t e d a t 7 0 d a y s , b u t fruits t h a t h a d r e c e i v e d a 2-h s o a k i n w a t e r a n d w e r e r e - d r i e d w e r e less r e s p o n s i v e a n d m o r e i n c o n s i s t e n t . A h y d r o p h i l i c c o m p o u n d ( s ) i n t h e fruit i s p o s t u l a t e d a s t h e causal a g e n t .