Mycorrhizal symbiosis is important for growth of coffee (
Mycorrhizae play an important role in growth and development of wild and cultivated plants. Genetic variation within plant species can influence both the degree of root colonization by mycorrhizal fungi and the response of the plant to mycorrhizal symbiosis [
Most classic studies on interactions between cultivars and AM fungi used colonization of mycorrhizal fungi within the root to quantify the fungal part of the symbiosis. However, Miller et al. [
Coffee is a key crop in the economy of many developing countries [
The objective of this study was to determine whether coffee cultivars differ in their interactions with AM fungi. Our hypothesis was that some coffee cultivars (
Soil samples associated with Caturra, Pacas, and Borbón cultivars were collected from three different sites in Puerto Rico. Samples were collected at Serrallés farm (Ponce), at Rullán farm (Adjuntas), and at Limaní (the UPR Agricultural Experimental Station, Adjuntas). These sites were chosen for uniformity in plant age, environment, and management.
A total of six soil samples per cultivar were collected on each farm as follows. Six rows were randomly selected from the area planted to each cultivar. Each sample consisted of five pooled soil cores; each core was 2.5 cm in diameter and 10 cm deep. The first core was taken at the midpoint between two neighboring plants in a row, and the other four were taken 15 cm from the first, forming an X. The soil was collected in plastic bags and transported to the laboratory on ice.
The pH was measured for each sample from Serrallés and Rullán farms using 3.0 g of soil mixed with 3 mL of ultrapure water. Dry to wet weight ratios were estimated using 20 g of fresh soil that was oven dried at 65°C for 7 days. Samples for mineral analysis were air-dried to constant weight and passed through a sieve with 2 mm mesh. Mineral content was determined at the Chemistry Laboratory of the International Institute of Tropical Forestry, USDA Forest Service. Available (extractable) mineral nutrient concentrations were estimated on a V-Beckman Spectraspan direct current plasma-atomic emission spectrometer using USDA IITF analytical lab protocols [
To test whether differences in mycorrhizae were correlated with differences in leaf nutrient content, ten leaves were collected from the fourth branch from the bottom of the two plants adjacent to each soil sample. Leaves were air-dried and ground using a Wiley Mill (1 mm opening) [
The soil cores were broken, homogenized manually and root fragments were removed. Hyphae were extracted as described [
The filters with hyphae were mounted on glass slides with immersion oil and observed at 400x [
For the samples from Serrallés farm, AM fungal spores were extracted from 100 g soil by the wet sieving and decanting method described by Pacioni [
Data for hyphal lengths, soil nutrient concentrations, and leaf elements were normally distributed. Differences among cultivars and replicates (farms) were analyzed by 2-way unbalanced ANOVA [
Mean hyphal length was lowest in Caturra at all three farms, and highest in Borbón on the two farms where it was grown (Figure
Extraradical hyphal length per gram of soil associated with coffee cultivars at three farms in Puerto Rico. Cultivars within each location were significantly different. Capital letters represent comparisons within locations and small letters differences within each cultivar among locations; bars with different letters are significantly different. Error bars show +1 s.d.
Most AMF examined had yellow, brown, or white globose spores greater than 54
Abundance (number
Soil pH values were similar among cultivars at Serrallés (pH 5.0) whereas the pH ranged from 4.4 under Caturra to 5.5 under Pacas at Rullán. Mg was the only soil mineral nutrient measured that differed significantly among cultivars (
Soil mineral concentrations at three coffee farms in Puerto Rico. Values are concentrations of extractable nutrients. Mean values are followed by standard deviations in parentheses. The first letter following each mean shows LSD differences among cultivars within a location, while the second shows differences among locations within the same cultivar. Values for the same element followed by the same letter were not significantly different (
Farm | Cultivar | P (mg/g) | Mn (mg/g) | Mg (mg/g) | C (%) | N (%) |
---|---|---|---|---|---|---|
Borbón | 0.46Aa(±0.10) | 0.47Aa(±0.29) | 1.96Aa(±0.48) | 2.36Aa(±0.11) | 0.21Aa(±0.01) | |
Limaní | Caturra | 0.49Aa(±0.13) | 0.22Aa(±0.06) | 1.75Aa(±0.53) | 2.65Aa(±0.48) | 0.22Aa(±0.03) |
Pacas | 0.43Aa(±0.10) | 0.83Ba(±0.83) | 0.45Ba(±0.08) | 2.00Ba(±0.19) | 0.18Aa(±0.00) | |
| ||||||
Borbón | 0.93Ab(±0.51) | 0.10Aa(±0.02) | 0.49Ab(±0.15) | 2.53Aa(±0.42) | 0.23Aa(±0.03) | |
Serrallés | Caturra | 0.89Ab(±0.31) | 0.13Aa(±0.02) | 0.56Ab(±0.07) | 4.03Bb(±0.23) | 0.19Aa(±0.17) |
Pacas | 0.86Ab(±0.18) | 0.12Ab(±0.02) | 0.50Aa(±0.06) | 3.46Bb(±0.19) | 0.31Bbc(±0.03) | |
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Rullán | Caturra | 0.55Aa(±0.28) | 1.08Aa(±0.65) | 1.43Ab(±0.32) | 6.33Ac(±1.66) | 1.55Ac(±0.90) |
Pacas | 0.49Aa(±0.15) | 1.29Ab(±0.37) | 1.13Ac(±0.28) | 4.50Bb(±1.48) | 2.28Bc(±0.68) |
All nutrients analyzed in leaves showed significant differences among cultivars at Limaní (
Mean leaf element concentrations in three coffee cultivars at two farms in Puerto Rico. Values in parentheses are standard deviations. The first letter following each mean shows LSD differences among cultivars within a location, while the second shows differences among locations within the same cultivar. Values followed by the same letter were not significantly different
Farm | Coffee cultivar | Ca (mg/g) | P (mg/g) | Mn (mg/g) | Mg (mg/g) |
---|---|---|---|---|---|
Borbón | 9.25A (±0.75) | 2.09A(±0.27) | 0.24A (±0.11) | 3.55A (±0.40) | |
Limaní | Caturra | 10.37Aa(±2.74) | 1.72Ba(±0.21) | 0.35Aa(±0.08) | 3.75Aa ( |
Pacas | 15.37Ba (±1.90) | 1.60Ba(±0.84) | 0.58Ba (±0.28) | 2.48Ba (±0.21) | |
| |||||
Rullán | Caturra | 12.83Ab (±2.42) | 1.47Aa(±0.49) | 0.40Aa (±0.15) | 3.90Aa(±0.73) |
Pacas | 10.39Bb(±0.75) | 1.66Aa(±0.20) | 0.21Bb(±0.07) | 3.16Bb (±0.32) |
Many common
Variation among cultivars and genotypes in dependence on AM fungi has been found in many crop plants [
In contrast, in other cases new cultivars showed higher mycorrhizal colonization than older cultivars. Cultivated varieties of tomato were found to be more responsive to AM fungi than wild accessions [
The mechanism by which Caturra, Borbón, and Pacas differ in AM extraradical hyphae is also unclear. Variation in plant responses to arbuscular mycorrhizal fungi may result from differences in the extent of fine root development [
Another explanation for the differences in hyphal lengths among cultivars could be different AM fungi associated with each cultivar. To assess this hypothesis we estimated numbers and diversity of spores in the rhizosphere of the three cultivars. Although we were not able to identify species, the morphotypes we found appear to belong to species of
Concentrations of P in soil can affect the interaction between mycorrhizal fungi and plants. High P concentration has been shown to inhibit AM fungal colonization of roots [
Although P concentrations in soil did not vary among cultivars within sites, leaf P concentrations were significantly higher in Borbón than in Caturra. The greater extent of extraradical hyphae in Borbón than in Caturra may have caused this difference in leaf P concentrations by facilitating P uptake. P concentration in plant tissue was correlated with their levels of mycorrhizal colonization in coffee [
Extraradical hyphal length in the soil is directly related to root colonization, though colonization rates can be a poor predictor of extraradical hyphal length [
In this study we found significant differences in AM fungal extraradical hyphal lengths among coffee cultivars within all three sites, and these differences were not directly attributable to soil nutrient concentrations. The results of this study can help to explain differences in cultivar responses to fertilization practices, and have implications for crop management.
Coffee researchers and growers in Puerto Rico have long observed that Caturra has a yield comparable to Borbón if fertilized, but a much lower yield than Borbón without fertilization [
The authors thank Mr. Rene Martínez, manager of Serrallés farm, Mrs. Melín Rullán, owner of Rullán farm, and Mr. Wigmar González and Álvaro Acosta, administrator and agronomist, respectively, of Limaní farm for access to the coffee plantations. This project was supported by FIPI and CREST-CATEC (HRD 0734826) programs at UPR. L. Lebrón received salary support through the Institute for Tropical Ecosystem Studies from the NSF Grants DEB-900002456 and DEB-9705814 to the University of Puerto Rico and the USDA Forest Service International Institute of Tropical Forestry (IITF) for Long-Term Ecological Research in the Luquillo Experimental Forest. The authors thank M.J. Sanchez, E. Lopez, and M. Santiago at IITF for assistance with chemical analyses, A.T. Mosquera for advice on soils and Rocío Rodríguez for guidance.