INTRODUCTION

Cashew (Anacardium occidentale L.) is a tropical shrub native to northeastern Brazil. It has been cultivated extensively in Central and South America, as well as Africa. The plant's primary products are the cashew nut, derived from the seed, and the cashew apple, a fleshy pseudofruit. The cashew apple, consumed fresh or processed, is rich in nutrients and possesses desirable sensory qualities, making it a valuable source of food and a potential ingredient for various products ^{(SAG, 2005}; ^{Mothé et al., 2017}). As a perennial species well-suited to tropical climates, cashew has emerged as a promising agricultural option for regions with low rainfall, offering a potential adaptation strategy to climate change ^{(SAG, 2005)}. It is a resilient crop capable of thriving in challenging environments, including soils with low fertility, salinity, and irregular rainfall (^{Bezerra et al., 2007}). The primary consumers of cashew nuts are the United States, India, and the European Union, with significant demand from countries such as the Netherlands, Germany, France, and the United Kingdom. India and Brazil historically have been the leading producers of cashews, followed by other notable growers, including Vietnam, Tanzania, and Indonesia (^{Coto, 2003}; ^{Bloomberg, 2016}; ^{Dendena & Corsi, 2014}).

Cashew (Anacardium occidentale L.) was introduced to Colombia in the 1960s, but its development has been relatively slow despite efforts by institutions such as the Colombian Agricultural Institute (ICA) and the Colombian Corporation for Agricultural Research (CORPOICA) (^{Méndez, 2017}). These organizations have identified significant potential for cashew cultivation in the country's semi-arid regions. Recent research has yielded promising results, including the development of three cashew genotypes: Corpoica Mapiria Ao1, Corpoica Yopare Ao2, and Corpoica Yucao Ao3. These genotypes exhibit favorable levels of productivity and resistance to anthracnose, making them suitable for validation in the Colombian Orinoquia region (^{Arango et al., 2018}). Additionally, recommendations have been established for the production of grafted cashew plants, enhancing the efficiency and quality of cultivation (^{Arango, 2020}). In recent years, several initiatives have been undertaken to promote the cultivation and export of cashew nuts in Colombia. One notable project is located in Puerto Carreño, Vichada, where efforts are focused on productive transformation and capacity building within the cashew value chain (^{Méndez, 2017}).

The nursery stage plays a critical role in the successful establishment and long-term health of cashew (Anacardium occidentale L.) plants (^{SAG, 2005}). While recommendations exist for producing grafted seedlings (^{Arango, 2020}), many farmers continue to rely on traditional nursery practices. Despite the cashew plant's resilience, improvements in nursery technology can enhance seedling quality and survival rates. Furthermore, there is a need for continued research and development to support the cultivation of cashews in Colombia, particularly about innovative agricultural practices and technologies (^{Orduz-Rodriguez & Rodríguez-Polanco, 2022})

While numerous studies have investigated the impact of organic fertilization on cashew (Anacardium occidentale L.) seedlings globally, including in Salvador (^{Salazar González, 2008}), Nigeria (^{Awodun et al., 2015}), Benin (^{Tokore Orou Mere et al., 2022}), and Tanzania (^{Valerian Mbasa et al., 2023}), limited research has been conducted on the effects of organic manure in Colombian cashew nurseries. To address this knowledge gap, this study aimed to compare the influence of two substrates on the emergence, morphometric characteristics, and phytosanitary status of cashew seedlings of the Mapiria and Yucao varieties in the municipality of Puerto Carreño, Vichada, Colombia.

MATERIALS AND METHODS

The research was conducted from January to June 2021 at "Apiarios La Cristalina,” located in Caño Negro, Dagua village, 45 km from Puerto Carreño, Vichada. Cashew seeds were obtained from fruits of the best quality and size, selected from elite fields (defined by high yield, disease resistance, and nut quality) of the "La Primavera" farm in Vichada.

An experiment was conducted under nursery conditions using a completely randomized design (CRD) with two-factor: (twp factors ??) fertilization with organic amendments and two varieties. The CRD was a 3 x 2 x 4 factorial design, with three fertilization treatments (30% chicken manure, 30% soil, and no amendment), two varieties (Mapiria and Yucao), and four repetitions.

The experiment had 480 bags of 5 kg each, 80 for each treatment and 20 for each repetition, which were randomly located and constituted the experimental unit.

The substrates with the treatments that were used were the following (Table 1):

The substrates were prepared using a nearby black soil from the Caño Negro region, mixed with river sand. Chicken and bovine manure, aged for over 30 days, were added in the proportions specified for each treatment

The seeds were sown while still attached to the false fruit. Additionally, a 1 cm-high layer of sand was added to each bag as a preventive measure to reduce the humidity of the substrate, which could prevent the attack of soil pathogens that affect the area.

Seeds, still attached to the false fruit, were sown into the substrates. A 1 cm layer of sand was added to each bag to reduce substrate humidity and prevent soil pathogen attacks.

Manual irrigation with a hose was conducted daily, with the frequency adjusted based on local rainfall.

A traditional phytosanitary management approach was employed, involving the application of fungicides to control diseases. The amount of irrigation and shade management in the nursery was adjusted to regulate soil humidity and mitigate high temperatures.

System of variables:

% of Emergency and % of Survival

% of Emergence= (Plants emerged / Total bags planted) *100” Equation 1

These data were taken during the first 3 weeks, from sowing.

The percentage of survival of the seedlings was also evaluated with the following formula:

% of Survival= (Surviving plants (day 55) / Total bags planted) * 100” Equation 2

To assess the effects of substrates and varieties on seedling growth, 20 seedlings per experimental unit (a single bag) were evaluated weekly. The following morphometric variables were measured:

Stem length: Measured from ground level to the point where the last pair of leaves emerged from the stem (in centimeters).

Stem diameter: Measured 1 cm from the base of the stem (in millimeters using a Vernier Caliper).

Number of leaves: Counted weekly.

Phytopathological variables

In the same experiment described above with six treatments, the phytopathological variables of incidence and severity of the diseases were evaluated as follows:

Incidence of the diseases: a record of the diseases was kept taking the number of affected plants and calculating as follows:

% Incidence = "Number of plants affected" / "Number of plants evaluated" "x100" (Equation 3) (^{Agrios, 2005})

The records began when the first symptoms of the diseases appeared on the plants.

Disease severity (for foliar diseases only)

The involvement of diseased leaf tissue was evaluated through the severity of the disease over time, using a six-grade scale (0=without symptoms, and 5= >75% of affected foliar area) (^{Ciba-Geigy, 1981}).

The severity per repetition was estimated with the formula described below:

"Severity (%) = " (∑axb))/kxN "x100" Equation 4 (Townsend & Heuberger) (^{Ciba-Geigy, 1981}), where:

a= symptom severity classes (0, 1, 2, 3, 4, and 5).

b=number of plants of each class.

k= maximum grade of the scale=5.

N=number of plants per experimental unit=10.

An analysis of variance of one factor (treatments) was performed with the emergence variables, survival, the four morphometric measurements, and the two phytosanitary variables (incidence and severity), for which the assumption of normality was verified with the Shapiro-Wilk test. The data in percentages were transformed into 2ArcSin √%/100 to achieve normality. The means were verified by Tukey's test with a 5% probability of error. The statistical package SPSS v21 was used.

RESULTS AND DISCUSSION

The ANOVA analysis revealed a significant influence of the manure amendment factor on emergence and survival (Table 2). However, neither the variety nor the interaction between variety and manure had a significant effect. Seedlings treated with chicken manure exhibited statistically higher emergence and survival rates (p<0.05) compared to those treated with bovine manure or the control group.

These results demonstrate the superiority of substrates with organic amendments over the control treatments. Both chicken manure (^{Montenegro et al., 2017}) and bovine manure (^{Arellano et al., 2015}) are excellent sources of organic matter with a rapid rate of mineralization, leading to the release of essential nutrients for seedling growth.

The ANOVA analysis revealed significant influences of manure amendments, varieties, and their interaction on morphometric variables at various time points from week 7 to week 9. Stem length was significantly influenced by amendments in weeks 7, 8, and 9, by varieties in weeks 5 and 7, and by the amendment-variety interaction in week 7. Stem diameter was significantly influenced by both amendments and varieties separately, as well as their interaction, in weeks 5, 7, and 9. The number of plant leaves was significantly influenced (P<0.05) by amendments and the amendment-variety interaction in weeks 5 and 7.

Table 3 presents the comparison of means for stem length and stem diameter between the manure treatments. For stem length, seedlings treated with bovine manure exhibited significantly higher growth (P<0.05) than those treated with chicken manure or the control in weeks 5 and 7. In week 9, both chicken manure and bovine manure treatments resulted in significantly longer stems compared to the control. Regarding the Mapiria variety, seedlings showed significantly longer stems (P<0.05) than the Yucao variety in weeks 5 and 7, but no difference was observed in week 9.

For stem diameter, seedlings treated with organic amendments (chicken or bovine manure) exhibited significantly higher values (P<0.05) than the control in weeks 5 and 7. In week 9, both manure treatments resulted in significantly thicker stems compared to the control. The Mapiria variety consistently demonstrated thicker stems (P<0.05) in weeks 5,7, and 9 (Table 3).

Table 4 presents the interactions between amendments and varieties for stem length and stem diameter. At week 5, the bovine manure treatments with both Mapiria and Yucao varieties exhibited the greatest stem length, significantly outperforming the chicken manure treatments and the control groups for each variety. Within the manure treatments, Mapiria with bovine manure had longer stems than Yucao with bovine manure, and Mapiria without amendments also had longer stems than Yucao without amendments. Similar results were observed at week 7, with the chicken manure treatments demonstrating the longest stem length. While there were no significant differences between Mapiria and Yucao interactions with amendments at week 7, both varieties outperformed their respective control groups.

Table 4 presents the interactions between amendments and varieties for stem diameter. At week 5, the bovine manure and chicken manure treatments with both Mapiria and Yucao varieties significantly outperformed the control groups for each variety. Within the manure treatments, there were no significant differences between Mapiria with bovine manure and chicken manure or between Yucao with bovine manure and chicken manure. However, Mapiria without fertilizer had a thicker stem than Yucao without fertilizer. In week 7, Mapiria with bovine manure demonstrated a significantly thicker stem than Mapiria with chicken manure or without fertilizer, while Yucao with bovine manure and chicken manure did not differ. The stem diameter of Mapiria with chicken manure and without fertilizer was significantly thicker than Yucao with chicken manure and without fertilizer, respectively. However, Yucao with chicken manure had a thicker stem than Mapiria with chicken manure. At week 9, Mapiria with bovine manure (0.56 cm) again exhibited the thickest stem, significantly surpassing Mapiria with chicken manure, without fertilizer, and Yucao with bovine manure (0.50 cm).

The observed differences in stem length between the varieties can likely be attributed to their genetic constitution and the known accelerated growth of cashew seedlings (^{Coto, 2003}). At the end of the 12-week nursery cycle, all seedlings in the organic fertilization treatments exceeded the recommended height of 19 cm for transplanting (^{Galdámez, 2004}). This demonstrates the adaptability of the cashew crop to the conditions of the Vichada area.

Stem diameter is a crucial quality variable and indicator of plant vigor, closely linked to subsequent productivity (^{Salazar González, 2008}). Seedlings treated with organic fertilizers consistently outperformed the control group for both Mapiria and Yucao varieties in weeks 3 and 5. However, in week 9, the chicken manure treatments with both varieties did not surpass the control. The threshold value of 0.5 cm, commonly used for forest and fruit species (^{Rueda Sánchez et al., 2012}), was not reached by Yucao with chicken manure or either variety without organic fertilizer. While these results highlight the relative advantages of chicken manure, previous research by ^{Salazar González (2008)} found that chicken manure did not increase the diameter of plants from a local cashew variety.

For the number of leaves per plant, seedlings treated with chicken manure exhibited significantly higher values (P<0.05) than those treated with bovine manure or the control at week 5. However, at week 7, both bovine manure and bovine manure treatments resulted in higher leaf counts compared to the control. By week 9, there were no significant differences between treatments, with all seedlings exceeding 14 cm in height. (Table 5)

Table 5 presents the interactions between amendments and varieties for leaf number. At week 5, Mapiria with chicken manure and Yucao with both amendments exhibited the highest leaf numbers. For Yucao, any organic fertilizer treatment resulted in more leaves than the control, while Mapiria with chicken manure had significantly more leaves (P<0.05) than with bovine manure or no amendment. At week 7, both Mapiria and Yucao with chicken or bovine manure had significantly more leaves (P<0.05) than the control groups.

In the final week, all seedlings had an adequate number of leaves, exceeding the recommended 14 photosynthetically active leaves for successful field survival (^{Corpoica y Asohofrucol, 2013}). These results demonstrate the vigor of both Mapiria and Yucao varieties under the unique edaphoclimatic conditions of Vichada, regardless of fertilization. This contrasts with a study in El Salvador, where, at the same age (63 days), only one of the 12 fertilized treatments reached 13 leaves, and the control had only 8.66 leaves (^{Salazar González, 2008}).

The positive results observed with chicken and bovine manure concerning seedling emergence, survival, and development can be attributed to their fertilizing properties, which improve soil physical quality and fertility. Chicken manure is relatively concentrated and fast-acting, providing organic matter and essential nutrients such as phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), and boron (B) (^{Montenegro et al., 2017}). Bovine manure is characterized by its high organic matter content (5.39%) and richness in macro-elements (nitrogen (N), phosphorus (P), calcium (Ca), magnesium (Mg), potassium (K)) and micro-elements (sodium (Na), molybdenum (Mo), iron (Fe), zinc (Zn), copper (Cu), boron (B)), also contributes significantly to seedling growth (^{Arellano et al., 2015}).

Organic amendments significantly influenced emergence, survival, and morphometric variables in cashew seedlings grown in a nursery. These findings align with ^{Arango's (2020)} assertion that substrate composition is crucial during the nursery stage, particularly for grafted seedlings. Arango recommended using 40% chicken manure in the substrate for this technology. Our results are consistent with previous studies conducted in various African regions demonstrating the benefits of organic fertilization on cashew seedlings (^{Awodun et al., 2015}; ^{Nduka et al., 2019}; ^{Tokore Orou Mere et al., 2022}; ^{Valerian Mbasa et al., 2023}).

Anthracnose, caused by Colletotrichum gloeosporioides Penz, was the only disease observed during the experiment. As noted by ^{Coto (2003)}, it is a common and harmful disease in cashew cultivation. Notably, damping-off, a concern for the technicians at "Apiarios La Cristalina," did not appear.

The absence of [disease name] could be attributed to low inoculum pressure, as this was a new nursery location. Additionally, the preventive measure of adding a 1-cm high layer of sand to all the bags may have contributed to disease control. To confirm these findings, further research should be conducted in the region.

Anthracnose was observed for the first time in the Mapiria variety in week 5, but by week 6 it was already present in Yucao. With the passage of time, a trend was observed towards a higher incidence of anthracnose in Mapiria than in Yucao, regardless of the substrate, reaching values of 52.5% y 30% respectively, at the end of the nursery stage.

ANOVA revealed significant effects of varieties and amendments on anthracnose incidence, and an interaction between these factors on severity in some weeks. Incidence was significantly influenced (P<05) by fertilizers in week 7 and by varieties in weeks 6, 7, and 8. Severity was significantly influenced by fertilizers in week 7, by varieties in week 9, and by the interaction of varieties and two factors in week 8.

Anthracnose incidence in cashew seedlings showed a significant statistical difference for amendments factors treatments only in week 7. Seedlings in the control group exhibited a lower incidence compared to those treated with chicken and bovine manure. However, varieties had a more pronounced effect. In weeks 7, 8, and 9, when the Mapiria variety consistently had a higher incidence (P<05) than Yucao (Table 6).

Anthracnose severity in cashew seedlings showed a significant statistical difference for amendment factor only in week 7. Seedlings in the control group exhibited lower severity compared to those treated with chicken and bovine manure. Comparing varieties, the Mapiria variety showed greater severity (P<05) than Yucao in week 9 (Table 6)

In week 8, Mapiria combined with chicken manure exhibited the highest anthracnose severity (11.0%), significantly differing from Mapiria without organic amendment and Yucao with chicken manure, but not from Mapiria with bovine manure (Table 7).

The importance of this disease is evidenced by the fact that, despite the phytosanitary management carried out in the nursery, as some authors have pointed out (^{Coto, 2003}; ^{Jiménez et al., 2014}), one-third or more of the seedlings were diseased. In the case of Mapiria with chicken manure treatment, it exceeded 50%. The results, to a certain extent, coincide with those of ^{Arango et al. (2018)}, who state that the three genotypes recommended for the Colombian-Orinoquia, Yoparo, Yucao, and Mapiria-are tolerant to anthracnose. However, they also point out that the percentage of attack by anthracnose at field conditions was 15.5% for Mapiria and 19.5% for Yucao.

High anthracnose severity in the nursery stage by week 9 poses a significant challenge for the phytosanitary management of cashew seedlings. This disease, which primarily affects new plant organs including flowers, can severely reduce plant production (^{Coto, 2003}; ^{Jiménez et al., 2014}). Nursery-stage infection suggests a high likelihood of severe anthracnose in the early plantation stages. Therefore, preventive measures are crucial to mitigate the disease's impact on crop productivity.

CONCLUSIONS

Initially, Mapiria and Yucao exhibited similar vigor. However, nursery conditions and organic amendments influenced emergence and survival. Bovine and chicken manure, as well as two varieties, affected stem length and diameter until week 7. Mapiria with bovine manure consistently yielded the best results for stem diameter. While leaf number was not influenced by varieties or treatments at the end of the nursery cycle, amendments and variety interactions influenced leaf number up to week 7. Anthracnose was primarily influenced by variety, with Mapiria being more susceptible to both incidence and severity.

Conflict of interest: The authors declare that they have no financial or personal interests that could have influenced the design, conduct, analysis, interpretation, or writing of this manuscript. All authors have contributed to the manuscript and reviewed its content, ensuring that no conflicts of interest compromised the validity of the results presented.