Plant and Soil 9 4 , 2 8 9 - 2 9 2 (1986).

�9 1986 Martinus Ni/hoffPublishers, Dordrecht. Pn'nted in the Netherlands. Ms. 6444

Varietal response to iron chlorosis in upland rice

c. KESAVA REDDY and G.V.S. SIVA PRASAD Division o f Plant Physiology, Directorate o f Rice Research Rajendranagar, Hyderabad 500 030 A.P., India

Received 11 June 1985. Revised November 1985

Key words Absorpt ion of iron Chlorophyll- induced chlorosis 1, 10-Phenonthroline

Summary In a s tudy involving twenty upland rice genotypes, the induct ion of iron chlorosis was found to be more by superphosphate application than due to lime incorporation into an alfisol soil under greenhouse condi t ions in GI tray-grown seedlings as quantif ied by two parameters viz., total chlorphyll content and Fe 2+ content . Of the two indices of iron chlorosis, Fe 2§ was more sensitive than chlorophyll content . Genotypes were grouped into efficient and inefficient categories both in te rms of absorpt ion and util ization of iron based on the degree of reduct ion in response to added superphosphate .

Introduction

Iron deficiency occurs f requent ly in calcareous soils and more so in drought prone areas 2"s'16,2z'2*'28 . Under rainfed upland condit ions rice crop of ten suffers from iron deficiency during the seedling stage due to aerobic condit ions which favours the oxidat ion of Fe 2§ to Fe ~*s'22. This ferric form precipitate and gets deposited on the root surface as ferric oxide and ferric hydroxides and prevent the entry of soluble ferrous iron into the root system 31'34 . As a result, the plant suffers from iron deficiency and exhibits chlorosis in young leaves ~4. Chlorosis does not necessarily indicate a deficiency of this nutr ient in the soil, but is indicative of the plant ' s inability either to absorb it f rom the soil or utilise it efficiently s'6. Such a deficiency is more c o m m o n in calcareous and alkaline soils than in acid or neutral soils. The lime-induced chlorosis does not seem to be due to free Ca 2. bu t due to high pH which lowers the solubility of ferrous iron 3'9. Factors like high soil moisture, poor aeration, high con- centrat ion of phospha te and heavy metals like Cu, Ni, Zn, Co, Mo, Cr; ext reme light intensity condit ions, root damage and viral incidence etc., have also been reported to cause iron deficiency 6,16, 22,23, 2 s, 27 "

Soil and foliar application of inorganic salts have been suggested for correcting iron deficiency 2"6'2~ However, under field conditions, the t rea tments are not effective, because the inorganic salts when applied to calcareous soils, of ten get rapidly inactivated. Foliar sprays of many compounds very of ten present serious precipitation probelms during application. Moreover, t iming of foliar sprays is very critical. Chelates, though effective, their large scale commercial usage has not taken place due to high cost. As such, the above practices have not gained wider acceptance.

There is ample evidence to indicate that by changing the plant to fit the soil, the problem could be economically solved 14.15'19"26"3~ . Such a genetic manipula t ion would almost certainly result in pe rmanen t benefi ts 3~ The various factors that differentiate an Fe-efficient genotype from less efficient ones were reviewed by several authors 5'6'9'22'a~ Based on these responses, a good number of screening techniques have been proposed to isolate Fe-efficient genotypes *'7's'2~ . In the present investigation, an a t t empt was made to see whether a relatively easy me thod can be followed to s tudy the genotype differences in Fe uptake and utilisation efficiency, so that a large number of genotypes can be screened by the breeders themselves. The results of a preliminary investigation are communica ted in this paper.

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Materials and methods

During the dry season of 1984, twenty upland cultures were sown in 100 • • 8 c m G.I. trays filled with an alfisol of pH 6.7 under greenhouse conditions. In each tray, 50kg of dry, pulverised soil was filled. There were three t rea tments in all viz., (i) lime (CaCO 3) treated (a~ 0 .5kg per 100kg soil, (ii) superphosphate treated @ 0 .25kg per 100kg soil and (iii) control. The above rates of lime and superphosphate were chosen based on a preliminary study. In the treated series, the added chemicals were thoroughly mixed with the soil. Each t rea tment was replicated twice. Application of lime and phosphorus were taken as main treat- ments and genotypes as sub- t reatments in a split-plot design. In each tray, the 20 genotypes were dry sown in rows of 5 cm apart and at 4 cm within the rows. The trays were then sprayed with water, sufficient to bring the soil to field capacity level (The field capacity of the soil was 27% on air dry soil basis). Thereafter, on every alternate day water was sprayed @ 5 1/tray till seedlings emergence. After germination, the seedlings were irrigated only twice a week, with 101 of water each time. When the seedlings were 4-week old, the trays were flooded with water to facilitate easy uprooting of seedlings for sampling purpose. From each genotype/ treatment/replicat ion, ten uniform seedlings were carefully uprooted. The seedlings were thoroughly washed in running tap water to remove soil particles adhering to the roots and were finally washed with distilled water. Surface water on the seedlings was removed by using blotting paper and the roots were cut-off at their base and discarded. The remaining part of seedlings were cut into two equal halves and their fresh weights immediately recorded. The terminal leafy port ion was utilized for est imating total chlorophyll con ten t with 80% acetone and the absorbance read at 652 nm on a spectronic 21 UVD spect rophotometer (Bausch and Lomb) 33. The basal port ion of the seedlings was utilized for est imating Fe 2. by the 1, 10-0- phenanthrol ine me thod and the absorbance read at 510 nm T M 8.

Results and discussion

In general, phosphate enr ichment of the soil increased the degree of chlorosis than lime enr ichment both in terms of Fe 2. and chlorphyll content . Between these two indices of chlorosis, Fe 2. con ten t seems to be more sensitive than chlorphyll content as could be seen from the mean percentage of reduct ion values and also from the reaction o f Lalmati and N 22, the two traditional upland cultures known for their Fe-stress subsceptibility under field con- ditions ~'12. On the other hand, lET 7580, an elite upland culture, which exhibits chlorosis under field conditions, did not suffer m u c h in te rms of Fe 2§ content , bu t its chlorophyll con- tent was sufficiently reduced, thereby indicating the problem of Fe 2. util ization rather than uptake per se. From the extent of reduction in the Fe 2§ and chlorophyll content , genotypes were broadly categorised into the following groups. (a) Efficient absorbers and utilizers. (b) Efficient absorbers but poor utilizers. (c) Poor absorbers but efficient utilizers. (d) Poor absorbers and poor utilizers.

The mean values of these groups of cultures in respect of Fe 2. and total chlorophyll content are given in Table 1.

The Fe-efflcient and Fe-inefflcient genotypes may differ in at least two respects viz., (i) at the uptake and translocation level, and (ii) at the utilization level. Major differences are at the absorption level wherein Fe-efficient plants respond positively and quickly to iron deficiency by releasing various reductants at the root surface to lower the root zone pH which favours the conversion o f insoluble Fe 3§ to soluble Fe 2§ They may also contain more citrate in the root sap 6. An Fe-inefficient genotype fails to exhibit a similar response under iron stress 6. At the morphological level also, genotypes may differ in their root charac- teristics ~4'19. At the utilization level, it seems that certain genotypes could fail to synthesise chlorophyll even when Fe 2. is supplied in large quanti t ies due to some metabolic defect as in the case of B-36, a mu t an t of BasmatP 5. The present results also indicate that genotypes differ

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Table 1. Total chlorophyll and Fe § content in different groups of upland cultures as in- fluenced by lime and phosphate t rea tments

Group Total chlorophyll % reduction * mg/g. fr. wt. over control

Control Lime Phosphate Lime Phosphate

A 0.608 0.483 0.317 20 48 B 0.604 0.388 0.259 38 58 C 0.577 0.428 0.339 25 40 D 0.528 0.352 0.220 35 58

Fe § (ug/g.ff wt) % reduction over control

Control Lime Phosphate Lime Phosphate

A 4.73 2.80 1.87 35 61 B 2.50 1.78 1.39 27 42 C 4.18 1.59 0.72 57 8l D 3.00 1.56 0.58 44 79

*particulars are given in the text.

at both absorption and utilisation levels. The details of causes for the differences at the utilization level are not yet clearly unders tood. Chlorotic plants seem to contain high P/Fe

ratio and the excess P may be responsible in inactivating Fe 2 § 10. React ions requiring Fe ~§ would suffer. Fur ther , under Fe-stress, different biomolecules varying in their stability and sensitivity to stress, may behave differently, as in the case of Catalase Vs Peroxidase 11'2~. Molecules with low stability may either fail to form or even easily gets decomposed so as to redistribute the available endogenous Fe 2§ among different ligands with still higher stability. The metabolic disturbances and adjustments , therefore seems to be more of quanti tat ive in nature.

The effect of added Ca 2+ on Fe 2§ seems to be more at the uptake level, probably by com- peting for the binding sites of chelating compounds , while that of super-phosphate seems to be both at the uptake and utilisation levels 1~ Superphosphate reduced Fe ~§ uptake by 60% compared to 45% by lime. Similarly, chlorphyll was reduced by 51% compared to 30% by lime. The relative degree of reduct ion in these two parameters was not uniform among different genotypes, the reasons for which are not yet clear. Fur ther investigations are necessary for a clear unders tanding of the mechanisms involved.

Acknowledgements We thank Dr U Prasada Rao, Rice Breeder for having kindly spared the valuable elite breeding materials for conduct ing the experiments . We also thank Dr R Seetharaman, Ex-Project Director and Dr JE Shinde, Project Director for their valuable suggestions while preparing this manuscript .

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