CHAPTER 4
IDENTIFYING TROPICAL FRUIT CROP NUTRIENT DEFICIENCIES
Introduction
The ability to identify deficiencies of plant nutrients before they affect tree vigor and limit crop yields is a major need in the production of tropical and subtropical fruit crops. This ability requires using a combination of diagnostic methods that enable intermediate steps to be taken before crop yields are severely reduced. Southern Florida has long been an area of tropical and subtropical fruit production and during the past fifteen years there has been a major increase in the area planted to specialty tropical fruits including carambola, lychee and papaya (J. H. Crane, University of Florida, personal communication). However, little research has been conducted to determine nutritional requirements of these crops and to identify, describe and verify nutritional deficiency symptoms in Florida. Leaf nutrient levels for carambola have been reported (Gálán Sáuco and Menini, 1993) but no visual descriptions have been reported and confirmed. Several studies have been conducted on the nutritional requirements of lychee in India (Mallik and Singh, 1965) and some observations have been made from controlled studies in Florida (Goldweber, 1959; Joiner, 1958). Foliar studies on the nutrition of papaya have been made in Hawaii (Awada, 1969; Awada and Long, 1969; Awada and Long, 1971a; Awada and Long, 1971b; Awada, 1977; Awada and Long, 1978; Awada and Long, 1980), Puerto Rico (Cibes and Gaxtambide, 1978; Pérez-López and Childers, 1982) and India (Nautiyal et al., 1986). However, other than data on the Hawaiian 'Solo' types, little information is available on the commercial 'Cariflora' cultivar grown in Florida.
The objectives of this investigation were to identify, document and verify visual N, K, Mg, Mn, Zn and Fe deficiency symptoms of carambola, lychee and papaya when grown under controlled conditions in greenhouse sand culture.
Materials and Methods
The study was performed under glasshouse conditions in Gainesville, FL using containerized carambola, lychee and papaya plants grown in sand culture. The mean greenhouse temperature was 86oF (82-105oF). Plants were chosen for uniformity of size and appearance. The carambola plants were obtained from Zill's High Performance Nursery (Boyton Beach, FL) and propagated by T-budding onto the industry standard rootstock cv. 'Gold Star'. The lychee plants were obtained from LNB groves, Homestead, FL and propagated by marcotting. 'Cariflora' papaya seeds were obtained from Lara Nursery & Farm, Homestead, FL and germinated in 24 cell polypropylene flats filled with fine sand. Six week-old papaya seedlings were selected for uniformity of size and appearance. All trees were repotted into 126 polypropylene pots (26 liter) containing white coarse silica sand (0.5-2.5 mm diameter). All selected trees were visually inspected for the presence of disease symptoms and pests in an effort to ensure that the induced deficiency symptoms were indeed due to nutritional anomalies.
In the bottom of each pot a plastic mesh screen was placed to prevent the sand from moving through the drain holes. Prior to potting, all polypropylene pots and the sand were washed with 10% H2SO4 and then thoroughly rinsed with de-ionized water. De-ionized water was also used for all base nutrient solutions. Fresh base nutrient solutions were prepared in 18 liter plastic containers prior to every application in order to minimize contamination and volatilization.
A modified Hoagland nutrient solution consisting of in g l-1: Ca(NO3)2, 1.10; (NH2)4SO4, 0.05; KH2PO4, 0.31; and MgSO4, 0.60. In addition 0.40 g l-1 of Fe (EDDHA) and Mn (MnSO4), Cu (CuSO4) and Zn (ZnSO4) were supplied at a concentration of 0.04 g l-1 (Hoagland and Arnon, 1938). Boron was added as H3BO3 at a rate of 0.004 g l-1. The pH of all solutions was adjusted to 6.0 with sodium bicarbonate added to buffer the solutions immediately before they were applied to the plants. Composition of the nutrient solutions minus specific nutrients consisted of a Hoagland nutrient solution minus N, K, Mg, Mn, Zn or Fe.
One liter of nutrient solution was applied twice weekly to each plant for a period of 30 weeks (September 25 - February 2, 1995). Prior to the start of the application of the omission treatments, each plant was given a complete nutrient solution treatment for two weeks. All nutrient solutions were applied to maintain field capacity, allowing the solution to only slightly drain through each pot. On days in which nutrient solutions were not applied, each potted plant was irrigated with 1 liter of de-ionized water which also was only sufficient enough to slightly drain through the bottom of each pot. Every two weeks each pot was completely flushed with de-ionized water to reduce the build-up of soluble salts. Observations were taken periodically on growth and leaf coloration as these advanced through progressive stages of development. As visual symptoms appeared, 35 mm slide images were taken to document specific nutrient deficiency symptoms.
Papaya stem diameter and height was measured at 3 cm above the soil level at the beginning and at the conclusion of the study. Leaf tissue samples from each plant were also collected either when deficiency symptoms appeared or at the conclusion of the study. Following collection the sampled leaves and petioles were rinsed with distilled water, sliced into pieces and immediately placed into paper bags to air dry then sealed to minimize potential contamination. Samples were oven dried for 72 hours at 70oC then ground in a Wiley mill to pass through a 20-mesh screen and stored in plastic bottles. Chemical determination was made on dried ground material. Analysis was determined by the Total Kjeldahl method (TKN) for N using an inductively coupled argon plasma spectrometer (Jarrel-Ash Model 61E ICAP), and by standard determination (Rapid Flow Analyzer - RFA) for the other elements under study (Hanlon et al., 1994).
Treatments included a complete modified Hoagland nutrient solution and modified Hoagland minus N, K, Mg, Mn, Zn or Fe. The seven treatments were replicated by two to six plants per treatment arranged in a completely randomized block design for each plant species. The data presented are means and the range of the two to six replicates for each treatment. Statistical analysis was by analysis of variance (SAS Institute, 1985) and means were separated using Dunnett's T test at the 0.05 level.
Results and Discussion
Carambola Leaf Analyses and Deficiency Symptoms. Symptoms of N deficiency appeared first in older leaves and included a loss of tree vigor, general leaf chlorosis (yellowing) and whole leaf stunting (Figure 4.1). Leaf N levels of the omission treatment were significantly lower than the concentrations of the complete treatment (Table 4.1). This may be due to the luxury consumption of N in the trees of the complete nutrient treatment. Potassium and Mg concentrations were also significantly decreased for the minus N nutrient treatment (data not shown).
Potassium deficiency symptoms first appeared on older leaves and included mottling, browning and death of leaflet margins and pronounced raised veins on the lower leaf surface (Figure 4.2). The K level of the minus K treatment was significantly lower than the concentrations of the complete treatment (Table 4.1). Fe was the only nutrient found to be significantly higher concentration in the K omission treatment than in the complete treatment (data not shown).
Symptoms of Mg deficiency first appeared on older leaves as a yellowing, browning and necrosis of leaflet margins (Figure 4.3). The lower leaflets on some leaves also dropped prematurely. Leaf nutrient levels of the minus Mg treatment were lower than complete treatment but not significantly. Although there were marked variations in the K nutrient levels of the plants grown under the omission of Mg, there were no significant difference between Mn, N, Fe and Zn (data not shown).
Symptoms of Fe deficiency first appeared on young leaves as intervenal chlorosis, as well as, a reduction of leaflet size. As symptoms progressed, leaves became light yellow or very pale, almost white in appearance with green veins (Figure 4.4). There was no
Table 4.1 Leaf macronutrient and micronutrient levels of 'Arkin'
carambola trees grown in sand culture.
Element Complete
treatment Omission
treatment
% on dry weight basis
Mean Range Mean Range
N 2.48 2.27-2.60 1.33z 1.16-1.65
K 1.76 1.48-2.07 0.25z 0.21-0.32
Mg 0.67 0.62-076 0.57 0.39-0.70
ppm
Fe 53 46-60 44 25-73
Mn 1016 810-1220 269z 174-411
Zn 161 99-188 38z 23-54
z Comparisons significant at the 0.05 level (Dunnett's T test).
significant difference between leaf Fe content of the complete and the minus Fe treatment. The low but insignificant levels of Fe may be due to the ability of Mn to replace Fe under extreme deficit.
No Zn deficiency symptoms were observed when Zn was withheld from the nutrient solution even though the nutrient levels were significantly lower (Table 4.1). This excessive concentration may be due to an abundance of available Zn in the applied complete nutrient solution.
No symptoms of Mn deficiency were observed despite the significantly lower nutrient concentration levels of the minus Mn treatment. This excessive concentration is most likely a result of luxury consumption of available Mn in the complete nutrient solution.
Lychee Leaf Analyses and Deficiency Symptoms. Symptoms of N deficiency of both 'Brewster' and 'Mauritius' cultivars began in older leaves as a lightening of leaflet color from dark green to light green to yellow (Figure 4.5). Leaflets tended to be stunted and some had slightly curled leaf margins and dropped prematurely. Young leaflets on trees subjected to prolonged deficiency were also stunted, chlorotic and dropped prematurely. New stems on severely deficient trees sometimes also defoliated. Leaf N levels of complete treatments for 'Mauritius' ranged from 2.31 to 2.93% with a mean value of 2.63%, whereas the N concentration of the omission treatment was significantly reduced (Table 4.2).
Symptoms of K deficiency of both 'Brewster' and 'Mauritius' cultivars included tip necrosis of the leaflets with the remaining area of the leaflets retaining a dark green color (Figure 4.6). Leaf K levels from trees given the complete nutrient solution ranged from 1.23 to 1.40% with a mean value of 1.31% for 'Mauritius'. The K concentration of the 'Mauritius' omission treatment was significantly lower than the complete treatment .
Symptoms of both 'Brewster' and 'Mauritius' Mg deficiency were small random necrotic spotting throughout the leaflets as well as tip necrosis (Figure 4.7). Leaf nutrient levels of both the 'Brewster' and 'Mauritius' complete treatment were not significantly different than the nutrient omission treatment. Although there was a significantly higher Zn nutrient level of the plants grown under the minus Mg, there were no significant difference between Mn, N, Fe, K and Mn (data not shown).
Deficiency symptoms of Fe of both 'Brewster' and 'Mauritius' trees began as intervenal chlorosis of younger leaflets (Figure 4.8). Leaf size was also reduced and premature leaf drop occurred. Severely deficient leaflets appeared to be very pale, almost white in color and eventually symptoms appeared on older mature leaflets as well. Iron levels of only the 'Mauritius' omission nutrient solution treatment appeared slightly lower than, but not significantly different from concentrations of the complete treatment.
Zinc levels of the omission nutrient solution treatment were significantly lower than concentrations of the complete treatment of both 'Brewster' and 'Mauritius' trees, although no Zn deficiency symptoms were observed. Mg was also found to be significantly lower in the minus treatment than for the complete treatments.
No Mn deficiency symptoms were observed on young 'Mauritius' or 'Brewster' lychee trees in the minus Mn treatment. However, the nutrient concentration for the omission treatment was significantly lower than the complete treatments (Table 4.2). Papaya Petiole Analyses and Deficiency Symptoms. Nitrogen deficiency symptoms of 'Cariflora' papaya leaves included a progressive change in leaf color from green to light green to yellowish green to completely yellow in color of only the older leaves (Figure 4.9). Omission of N also reduced the size and shape of the leaves. However, there was no significant difference among N petiole nutrient levels of either the complete or omission treatment (Table 4.3). In general, nutrient levels of the leaf lamina were higher and more variable than the petiole levels for all the elements (Table 4.3). This was consistent with what researchers in Hawaii have found (Awada and Long, 1971a). From their work it was found that analysis of papaya petioles were a more reliable indicator of plant nutrient status than papaya leaf tissue.
Potassium deficiency symptoms were quick to appear on the mature leaves and included pronounced raised veins on the undersides of leaves, dark green color, and strap-like distortion to the lobes of the leaf (Figure 4.10). There was no significant difference among N petiole nutrient levels of complete and minus N treated plants (Table 4.3). The potassium nutrient concentration was significantly lower in leaf and petiole tissue of the minus K treatment (Table 4.3). Potassium nutrient levels were significantly lower in the minus K treatment. In general, nutrient levels were lower in petioles of the nutrient omission treatments than in petioles of the complete treatments.
Magnesium deficiency symptoms of 'Cariflora' papaya appeared first in the older leaves and included mottling (light yellow and dark green areas) which sometimes coalesced forming larger chlorotic areas and general chlorosis with intervenal areas remaining green (Figure 4.11). Magnesium was found to be significantly lower for both the leaf and petiole analysis of the omission treatments (Table 4.3).
Iron deficiency symptoms of 'Cariflora' papaya first appeared on younger leaves and included gradual intervenal chlorosis and stunting of leaves (Figure 4.12). Papaya petiole and leaf Fe levels of the omission treatment were lower in concentration than the complete treatment but not significantly reduced (Table 4.3).
Zinc deficiency symptoms of 'Cariflora' papaya included pronounced raised, light green veins on the upper and lower leaf surface, distorted strap-like leaf lobes, and a slight yellowing of the youngest leaves (Figure 4.13). Leaf and petiole levels of the omission treatments were lower than the complete treatment but not significantly reduced (Table 4.3).
Symptoms of Mn deficiency included yellow mottling to severe chlorosis of older leaves (Figure 4.14). Leaf and petiole nutrient levels of the omission treatment were not significantly reduced, although the mean of the minus Mn treatment were lower than the complete treatment (Table 4.3).
Symptoms of B deficiency are suspected to have appeared in two replications of the control treatments even though adequate amounts were applied in the complete nutrient solution. A peculiar malformed, thickened appearance of the leaves with a stunted bunchy growth symptom of the apical meristem were exhibited similar to visual symptoms reported by Cibes and Gaxtambide (1978). Boron deficiency symptoms have not been characterized for papaya leaves in Florida and has not been recognized as a deficiency problem for papaya production in Florida.
Papaya Diameter and Height Growth. Lack of N had a pronounced effect on the growth of trees, in all cases the trees grown with the minus N treatment were severely stunted when compared to healthy trees given the complete nutrient solution. The greatest reduction
Table 4.4 Effect of nutrient omission on diameter and height growth of 'Cariflora' papaya trees grown in sand culture.
Treatment Diameter
(mm) Height
(cm)
Complete 35.65 (+ 3.36)y 121.17 (+ 17.51)y
- N 14.18z (+ 1.37) 49.58z (+ 6.26)
- K 22.78z (+ 4.27) 83.83z (+ 12.26)
- Mg 33.22 (+ 3.44) 110.92 (+ 18.75)
- Fe 33.78 (+ 3.47) 131.00 (+ 19.64)
- Mn 34.92 (+ 2.89) 120.83 (+ 10.91)
- Zn 28.37z (+ 3.75) 120.08 (+ 13.83)
z Comparisons significant at the 0.05 level (Dunnett's T test).
y Standard deviation in parentheses.
in stem diameter growth was observed with the minus N treatment (Table 4.4). The second largest significant reduction in diameter was caused by the absence of K. The decrease in total diameter growth due to the lack of Zn was ranked third, but was not significant. Papaya stem diameter and tree height was significantly reduced for the minus N and K treatments compared to their respective complete treatments (Table 4.4). The minus Mg, Fe, Mn, and the complete treatment did not result in any significant decrease in either diameter growth or height.