Evaluation the durable resistance of soybean varieties toward leaf rust caused by Phakopsora pachyrhizi

The main disease of soybean plants is leaf rust caused by the fungus Phakopsora pachyrhizi which can cause a decrease in the yield of up to 60% and has the potential to reduce seed quality. The use of resistant varieties is the main component of rust disease control. The purpose of this research was to determine the resistance level of several soybean varieties to the rust disease caused by Phakopsora pachyrhizi and its effect on the production of each variety. To evaluate the resistance reaction of soybean varieties to rust disease, the IWGSR system was used, as the intensity level of the disease and its effect on the production of each tested soybean variety. The results showed that the Detap 1 variety counted the lowest disease intensity of 22.84% with a susceptible disease reaction and had high productivity, followed by the Agromulyo, Anjasmoro, and Devon 1 varieties which categorized a mildly susceptible disease reaction with a disease intensity of 25.34%, 27.46%, and 28.70% respectively. The Derap 1 and Edamame varieties have a high disease intensity of 35.18% and 29.31% with susceptible disease reactions. The production of the highest number of pods was the Agromulyo variety.


Introduction
Soybean have special characteristics that they can grow upright, have dense leaves, look like bushes, and have various morphologies because soybean is an annual crop.Soybeans included in cultivars with wide leaf characteristics have better sun absorption with higher yields if compared with soybeans included in narrow leaf cultivars [1].
Leaf rust disease is an important disease in soybean plants which occupies the first level of various diseases causing decreased soybean yields to a level of 30-60% damage and has the potential to reduce the quality of soybean seeds.In addition, this disease attack will make soybean seeds and seeds smaller.Symptoms of soybean rust disease are clearly visible on the leaves, stalks and sometimes on the stems.At first there are small gray spots that will gradually turn dark brown.Spots of rust are visible before the postule (ulcers) rupture [2].The characteristics of several soybean varieties are as follows [3]: i) Anjasmoro variety is included in the national superior variety category released in 2001, a mass selection from the pure Mansuria strain population.Purple hypocotyl, purple flower, yellow seed coat, plant height 64-68 cm with branches 2.9-5.6.The protein content in soybeans of this variety ranges from 41.78-42.05%,has a yield of 2.25 tons/ha, and 100 grams of seed weight is 16 grams.Resistant to dropping and splitting of pods for moderate leaf rust resistance.ii) The Agromulyo variety comes from Thailand introduced by PT.Nestle Indonesia in 1988 with the original name Nakhon Sawan I, has the characteristics of a purple hypocotyl, purple flower, yellow seed, and the yellow seed coat, 40 cm plant height with 3-4 branches.The protein content of this variety is 39.4%, has a yield of 1.5-2.0tons/ha, and the weight of 100 seeds is 16 grams.Resistant to falling, the resistance to leaf rust is moderate.
iii) The Derap 1 variety was released in 2018, derived from cross-selection G511H with Anjasmoro has the characteristics of a purple hypocotyl, green epicotyl, purple flower, yellow pod skin, and yellow seeds.Protein content ± 39.17%, has a yield of 3.16 tons/ha, and the weight of 100 seeds is 17 grams.Moderately resistant to damping, splitting of pods, and leaf rust.iv) The Detap 1 variety was released in 2017, derived from the selection of a cross G551H with anjasmoro, which has the characteristics of a purple hypocotyl, green epicotyl, purple flower, round, and large seed shape.[4,5].
Symptoms of rust disease initially develop on the leaves of the plant, the characteristic of the affected plant is the presence of small spots that will turn brown on the underside of the leaves.These little dots are the uredospore-producing uredium.The initial attack will cause the leaves to turn yellow and then turn brown and fall and empty the pods.Small gray-brown spots will turn dark brown, rusty spots will appear if the boils (pustules) break.If the spots are near the veins, they will look angular because they are limited by the veins.The attack will begin to appear on the lower leaves and then on the younger leaves.In general, rust spots begin to appear when the plants are 25-40 days old [6].
The main method of controlling Asian Soybean Rust (ASR) is the use of chemical fungicides, which minimize disease damage, but increase production costs and environmental problems.One way to increase soybean production is to plant disease-resistant soybean varieties which can reduce soybean production.One way to obtain disease-resistant varieties is to determine disease intensity and plant productivity [7,8].
Data on the resistance of several soybean varieties (Glycine max) which are dominantly grown in Indonesia to leaf rust disease (Phakopsora pachyrhizi) is needed to determine its relationship to soybean productivity.

Materials and methods
The tools used in this research were hoes, polybags 35 cm x 35 cm, measuring cups, and brushes.The research materials were Aquades, soil, soybean seeds of the Anjasmoro Variety, Agromulyo, Derap 1, Detap 1, Devon 1, Biosoy, Edamame, NPK fertilizer, and manure.Seeds were selected by soaking the seeds in water for 5 minutes.Preparation for planting was carried out by filling a 35 × 35 cm poly bag with soil that had been mixed with manure 2:1.Filled polybags are put into the greenhouse and arranged according to the repeated plan.At the age of 21 DAP, fertilization was carried out using NPK fertilizer at a dose of 5 grams/polybag.
Phakopsora pachyrhizi urediniospores suspension was prepared in the laboratory.Plants infected with rust disease naturally in the field are used as a source of inoculum.Infected leaves are incubated for 1-2 days.After that, the resulting spores were taken using a brush and then suspended using distilled water until a density of 106 was obtained.Inoculation was carried out on plants aged 3 WAP in the morning by spraying the spore suspension onto the leaf surface.
Observation of disease intensity was carried out for four weeks on soybean plants aged 7 WAP, 8 MST, 9 WAP, and 10 MST.The observation parameters in this study used the IWGSR (International Working Group of Soybean Rust) system combined with the INTSOY system (the second number represents the spot density of 1 cm 2 on soybean leaves and was given a score), calculating disease intensity values, number of pods, seed 100-grain weight.Observations according to the IWGSR system according to [9] are as follows: a.The first digit represents the position of the soybean leaf Score 1 is 1/3 of the leaf in the lower position, Score 2 is 1/3 of the leaf in the middle position and Score 3 is 1/3 of the leaf in the upper position b.The second number represents the density of rust spots on the leaves Score 1 for No rust spots, Score 2 for Few rust spots (1-8 spots/cm), Score 3 for Moderate rust spots (9-16 spots/cm) and Score 4 for Lots of rust spots (more than 16 spots/cm) cm).c.The third digit represents the leaf's reaction to rust disease Score 1 for without pustulate (spots), Score 2 for spots without spores and Score 3 for spots with spores (uredospores) 1.The intensity of leaf rust disease is calculated using the formula: The response of soybean genotypes to leaf rust disease was assessed based on the intensity of the disease in percent (%) as follows.

Reaction to Fungus Rust (IWGSR)
[111] stated that there is a dominant gene that controls the resistance of soybean plants to leaf rust disease.It is suspected that the derap 1 variety does not have this resistance gene, so the response to leaf rust disease is different for each variety.This is in line with the statement [12] which states that there are differences in the response of each soybean variety to create conditions that can inhibit and slow down the infection of pathogens that live in resistant plants.The results of the observations in table 3 show that the attack intensity of the fungus Phakopsora pachyrhizi tends to increase with increasing plant age.The highest attack intensity for each variety occurred 10 weeks after planting.At the time of the last observation, it was seen that the second variety had the lowest attack intensity value of 22.84%.and derap 1 variety has the highest attack intensity values, namely 35.18% each.

Attack intensity
The intensity of the disease tends to increase with the increasing age of the plant.The highest disease intensity occurred in all varieties at the age of 78 days after planting.According to [4] that the older the soybean plant, the more susceptible it will be to Phakopsora pachyrhizi attack because plant growth greatly determines the virulence of the pathogen in addition to supporting environmental factors.The results of the observations in table 4 show that the production number of pods per plant has different results for each variety.The production of the highest number of pods was the agromulyo variety which was 45.33 compared to other varieties, namely the anjasmoro variety at 37.56, the detap 1 variety at 21.33, the devon 1 variety at 15.17 and the edamame variety at 10.78 while the lowest pod production per plant was the 1 derap variety was only 10.33 pods.

Production of pods
The agromulyo variety has the highest number of pods produced because this variety has the characteristics of very small seeds so more and more pods are formed.while the detap 1 variety had the highest average seed weight per plant and 100 seed weight.This is in line with the intensity of the disease in the stage 1 variety which is the lowest disease intensity compared to other varieties.According to [13], the number of leaves is an indicator of growth as well as a parameter that can describe the ability of plants to carry out photosynthetic activities.
Detap 1 varieties with low disease intensity resulted in leaves that did not fall so that the leaves were more optimal in carrying out photosynthesis as an indicator of increasing plant seed production, this was by the opinion [14], which stated that an increase in seed weight per plant and 100 seed weight also related to an increase in the number of leaves of soybean plants, this can happen because, with an increase in the number of leaves, more light can be captured so that the opportunity to increase the process of photosynthesis and the assimilating process which is translocated to the seeds will also increase.Observations in table 5 showed that the weight production of 100 seeds of the first variety had the highest yield of 21.00.For varieties of anjasmoro 15.00, agromulyo 13.17, derap 1 11.67, and edamame 17.06.Meanwhile, the Devon 1 variety, 9.78, was the lowest yield among other varieties.This is in line with the opinion [15] which states that the lower the disease intensity, the higher the production.The Devon 1 variety is influenced by morphology so the weight production of the plants is low, this is because this variety has fewer seeds and the weight on the seeds is relatively low, therefore the Devon 1 variety has a very low average weight yield.
In addition to photosynthetic factors, genetic and environmental factors can also affect the yield or weight of plant seeds.This is by the opinion [16], each variety has genetic differences that can cause differences, and environmental conditions such as humidity and temperature in the greenhouse also affect soybeans.

Conclusions
In the research that has been done, it is concluded that there are differences in the different responses of all the tested varieties to leaf rust disease caused by Phakopsora pachyrhizi. 4 varieties, namely Detap 1, Agromulyo, Anjasmoro, and Devon 1, are classified as having a somewhat susceptible reaction and 2 varieties are classified as susceptible, namely Derap 1 and Edamame.The detap 1 variety had the lowest disease intensity value of 22.84% with a somewhat susceptible disease reaction and high productivity, followed by the Agromulyo, Anjasmoro, and Devon 1 varieties which had a moderately susceptible disease reaction with a disease intensity of 25.34% respectively; 27.46% and 28.70%.The Derap 1 and Edamame varieties had a high disease intensity of 35.18% and 29.31% with susceptible disease reactions.The production of the highest number of pods was in the Agromulyo variety and the highest weight production of 100 seeds was in the Detap 1 variety.
of leaves attacked on each scale value v = Scale value for each leaf N = Total number of leaves Z = Highest scale value The attack category/score for the disease are [10]: 0 = No attack 1 = 0-10% of the affected leaf surface area 2 = 10-20% of the affected leaf surface area 3 = 20-40% of the affected leaf surface area 4 = 40-60% of leaf surface area affected 5 = 60-100% of leaf surface area affected 1230 (2023) 012111 IOP Publishing doi:10.1088/1755-1315/1230/1/0121114 The protein content is ±40.11%, the yield potential is 3.85 tons/ha, and the weight of 100 seeds is ±15.37 grams.Fairly resistant to lodging and splitting of pods, resistant to leaf rust disease.Phakopsora pachyrhizi is a major disease in soybean plants that occurs during the dry season.The spread of rust disease started from Japan and East Asia in 1902, entered Southeast Asia and Australia in 1914, reached India in 1950, and Hawaii in 1994, then to South Africa in 1920 and reached Uganda in 1996.In 2001-2002, rust disease spread to South America and in 2004, it spread to the United States

Table 1 .
The reaction of soybean varieties to leaf rust fungi based on the IWGSR system.

Table 2 .
The reaction of soybean varieties to Phakopsora pachyrhizi fungus based on the IWGSR Rating System.

Table 2
has different results for several types of varieties.

Table 3 .
Average intensity of Phakopsora pachyrhizi disease on soybean plantson each observation.
Note: Numbers followed by the same letter in the same column and row are not significantly different at the HSD level test of 0.05

Table 4 .
Production of pods on soybean varieties affected by Phakopsora pachyrhizi.
Note: Numbers followed by the same letter in the same column and row are not significantly different at the HSD level test of 0.05

Table 5 .
Production of 100 dry seeds on affected soybean varieties Phakopsora pachyrhizi.Numbers followed by the same letter in the same column and row are not significantly different at the HSD level test of 0.05 Note: