Intensity of Leaf Rust Disease on Four Robusta Coffee Clones in Natar, South Lampung

Lampung Province is the producer and exporter of coffee in Indonesia. Leaf rust disease is an important disease in coffee and is caused by fungus Hemileia vastatrix Berk & Br. This disease has spread to all coffee cultivation areas worldwide, including Indonesia. The incidence of this disease can cause production losses and reducing productivity up to 50%. The aim of the study was to determine the intensity of leaf rust disease in four Robusta coffee (Coffea canephora) clones in Natar, South Lampung Regency, Lampung Province, namely BP 436, BP 534, BP 939 and SA 203. The experiment was conducted in a completely randomized block design, with four clones, 30 replicates, and 30 evaluation samples. The intensity of disease attacks was calculated using Townsend-Heuberger formula. The results indicated that the intensity of disease attack on four clones was classified as a mild attack, with the lowest attack level was on BP 534 clone (5.63%). Robusta coffee is relatively tolerant to leaf rust disease, however management of this disease must be applied to prevent greater yield losses.


Introduction
Coffee (Coffea canephora) is an export commodity with high economic value, and is a leading commodity in Indonesia.The export value of Indonesian coffee in 2022 was 434,190 tons, an increase of 12.92% from the previous year, with a total export value of USD 1.13 billion [1,2,3].Lampung Province is the producer and exporter of coffee in Indonesia.Lampung is one of the coffee producing centers in Indonesia with an area of 156,395 ha, with a production of 122,053 tons in 2022 [4,5].Most of the coffee plantations in Lampung are smallholders and lack of assistance in cultivation technology, including pest and disease control.Pests and diseases can cause damage to plants and can cause yield losses in quality and quantity, therefore causing economic losses.
Leaf rust disease in coffee caused by the fungus Hemileia vastatrix Berk & Br., is an important disease of coffee plants in the world that infests Arabica and Robusta coffee.This disease has been found in Indonesia since 1876, which destroyed most of the coffee plantations [6,7,8].Coffe leaf rust can cause problems in all coffee-producing regions and can reduce production by 20-70%.The fungus attacks coffee plants in nurseries and mature plants [9].
The Ministry of Agriculture has released many coffee clones, including Robusta coffee clones, namely BP 436, BP 534, BP 939 and SA 203 which are cultivated in Natar, South Lampung Regency, Lampung Province.There have been no reports on the intensity of coffee leaf rust in Lampung, especially the disease that attacks the four clones.Information regarding disease intensity values is important for designing appropriate control strategies.The purpose of this study was to determine the intensity of leaf rust disease on four Robusta coffee clones in Natar, South Lampung.

Characteristics of the study area
The study area was on dry land at the Research Station of Assessment Institute for Agricultural Technology, Natar, South Lampung District, Lampung Province, Indonesia in a total area of 5 ha.Natar is located in Sumatera Island, West Indonesia, at an average altitude of ±100 m above sea level, and are characterized by a mean annual rainfall of 268.33 mm/month, humidity 86% and a mean annual temperature of 28 ºC, with Red Yellow Podzolic soil type, pH<6 (acidic) [10] (Figure 1).The coffee plantation in Natar was well maintained technically.Pruning and weed control was carried out regularly.

Design
Four Robusta coffee clones were used in the study, namely BP 436, BP 534, BP 939 and SA 203.The experiment was conducted in a completely randomized block design, with four clones, 30 replicates, and 30 evaluation samples per replication.The observations were determined on leaves of coffee.The infestation of the leaf rust disease was observed randomly by measuring the severity of leaf rust with diagrammatic scales described by Figueiredo et al. [11].

The intensity of disease attacks
The intensity of disease attacks (I) was calculated using Townsend-Heuberger formula [12]: I (%) = ∑ (ni x vi) / N x V, where i is the number of category, ni is the number of plants in one category, vi is the damage category, N is the total number of plants observed, and V is the highest score.Based on the calculation results using the above formula, leaf rust disease is categorized as a mild attack if I ≤ 25%, moderate if 25% < I ≤ 50%, severe if 50% < I ≤ 75%, and very severe if I > 75%.The intensity of attack values were analyzed by analysis of variance (ANOVA) and the significant differences among means was compared with Duncan's test (P<0.05).

Result and discussion
The leaf rust disease symptoms are presented in Figure 2. The symptoms can be observed on the upper and lower surfaces of the leaves, marked by yellow-orange powdery spots.Infected leaves develop yellow spots, then turn brown.Light yellow spots appear on the underside of the leaves, then turn dark yellow, powdery orange, which is the uredospore of the fungus H. vastatrix.The intensity of leaf rust disease attacks are presented in Table 1.The intensity of leaf rust attacks on leaves ranged from 5.63 to 18.47%.The leaf rust disease attack on the BP 534 clone was showed significantly lower than that on the other clones.The infestation of this disease on the leaves of the BP 436 clone was the highest compared to the other clones.However, the results indicated that the intensity of disease attack on four clones was classified as a mild attack.Robusta coffee is relatively tolerant to leaf rust disease, however management of this disease must be applied to prevent greater yield losses.Factors that influence disease development are environmental, including temperature, humidity, rainfall, and sunlight.The optimum temperature for disease development is 21-25°C.Rain plays a role in increasing humidity making it suitable for the germination of uredospore and the spread of the fungus H. vastatrix.Direct sunlight hits the leaf surface, inhibiting the germination process of uredospore and extending the incubation period of leaf rust disease.Uredospore spread through rain, wind, insects such as thrips, birds and humans [9].The population genetics and incidence of leaf rust disease was estimated original sources and subsequent migration pathways of wind-borne spores in three main coffee production areas in Vietnam [13].
The level of leaf rust attack on four Robusta coffee clones in Natar was classified as mild attack.This could be because Robusta coffee is genetically more resistant to rust than Arabica coffee.Coffea canephora is a species introduced because of its rust-resistant qualities and greater strength and productivity than C. arabica, therefore it is called Robusta [14].Natar is located in the lowland.The condition of the plantations in the Natar coffee plantation is well maintained technically.Pruning and weed control is carried out regularly, reducing humidity, thereby minimizing disease infestation.
The BP 534 clone was the most tolerant of leaf rust disease in this study.This clone is a coffee clone as a result of individual selection on the Robusta coffee population in the Tugusari plantation, wide adaptability to various altitudes and climate types, with high yields [15].These results can be used as the basis for the development of coffee clones, including hybrid coffee that is more resistant to pests and diseases with high yields.
Recommendation for the management of leaf rust disease include: (1) the use of resistant/tolerant varieties; technical control includes weeding, fertilizing, pruning, and shade management; maintain good overhead shades in the new clearings; biological control using beneficial microorganism; increase the diversity and abundance of insects pollinator with flowering plants; control with botanical pesticides such as coconut shell liquid smoke; control with chemical fungicides or Bordeaux mixture; reduce humidity by reducing watering, spacing the roof shade so that direct sunlight can enter; sanitation by cutting diseased leaves and then burning them or burying them in the ground [9,16,17,18].

Conclusion
The intensity of leaf rust disease attack on four clones was classified as a mild attack, with the lowest attack level was on BP 534 clone.These results can be used as the basis for the development of coffee clones, including hybrid coffee that is more resistant to pests and diseases with high yields.The four Robusta coffee clones were relatively tolerant to leaf rust disease, however management of this disease must be applied to prevent greater yield losses.

Figure 1 .
Figure 1.Map showing the location of the coffee plantation in Natar, South Lampung.

Figure 2 .
Figure 2. (A) Diagrammatic scale to assess the severity of coffee leaf rust leaves [10]; (B) The leaf rust disease symptoms in Robusta coffee clones in Natar, South Lampung.

Table 1 .
The intensity of leaf rust disease attacks on Robusta coffee clones in Natar, South Lampung.The values followed by the different letters in each columns are significantly different at P<0.05 by Duncan.