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Crop-Set™ is categorized as a natural biostimulant by virtue of the fact that it contains a plant extract belonging to a group collectively known as saponins, which have the ability to influence hormonal activity in plants. Crop-Set™ has been used in the citrus industries of the US, Brazil and South Africa for several years. The most extensive use has been in South Africa, where its application commenced almost seven years ago. The product has been used in the citrus industries of Brazil and the US (California, Florida and Arizona) for almost four years.

To be categorized as a biostimulant a compound must be able to influence the hormonal activity of a plant. Not all biostimulants are natural. For example, the following products are also used as plant growth regulators: benzyladenine (Accel) is a highly reactive synthetic cytokinin; trinexapac-ethyl suppresses gibberellin biosynthesis; gibberellic acid (GA3 – ProGibb) and prohexadione calcium (Apogee – a GA biosynthesis inhibitor); propiconazole is a fungicide with growth regulatory properties; and potassium silicate, which also enhances plant growth.

Natural biostimulants such as those derived from saponins, humic acid and seaweed, are more userfriendly and less likely to become restricted by marketing agencies and consumers. The quality control procedure that Crop-Set™ is subjected to makes it unique among other natural biostimulants.

This fact results in the effects being consistent and not fluctuating from season to season.

Significant research on the effect of saponins on the growth of plants was conducted by the French plant physiologists Balansard and Pellessier in the 1940s. They made several significant discoveries viz.: (i) saponins reduced the surface tension of tissues and modified the cellular permeability of seed; (ii) low concentrations of saponins stimulated rapid root development, precocious bud formation and increased chlorophyll production and photosynthesis; (iii) seed treatment with saponins affected all stages of growth of plants e.g. seed germination, vegetative, floral and fruiting stages. These researchers concluded that the effect of saponins was analogous to that of true plant hormones, cytokinins, auxins and gibberellic acid (Balansard and Pellessier, 1943; 1944; 1945). Saponins therefore affect plants at the cellular and morphogenetic levels.

Biostimulants not only affect internal plant hormone levels but also promote the production of antioxidants. Research has shown that environmental stresses such as drought, ultraviolet light, herbicide use, high soil salt content and heat damage plants by causing production of free radicals or reactive oxygen molecules. These molecules are strong oxidizing agents and damage lipids, proteins and DNA inside the plant cells. Antioxidants are metabolites and enzymes that scavenge free radicals and thereby protect plant cells from damage (Zhang and Schmidt, 1999).

Studies by plant physiologists in Brazil (Medina, 2003) and South Africa (J. Bower, personal communication) have identified the same reactions observed by Balansard and Pellessier following the application of Crop-Set™ to citrus trees. These include enhanced lateral bud development, stem elongation, enhanced root development, enhanced flower initiation, increased fruit size and weight, increased juice content, enhanced color and reduced heat stress. The effects at the cellular level include increased cell division, increased elasticity of cell walls, re-direction of photo-assimilates to fruit, increased chlorophyll production, reduced absicissic acid levels, increased uptake and mobilization of nutrients (in particular calcium) and suppression of the effect of viruses on yield and fruit size (Jameson, 2000).

This paper summarizes the results of field trials with Crop-Set™ in citrus orchards located in Arizona, California and Florida during the 2002-2003 season.


Materials and methods

DOSAGE RATE

In all cases the dosage rate was a total of 16 oz per acre. The amount of water used per acre varied from grower to grower, but was never less than 50 gallons per acre when applied using a mist-blower type spray rig.


TIMING OF APPLICATION

Crop-Set™ applications in sweet oranges and mandarins were applied at petal-fall and when fruit was golf ball size. The timing of applications in the lemon trial in Arizona differed from that of the sweet orange and mandarin studies. In one trial Crop-Set™ was applied at a rate of 16 oz per acre at petal-fall and in the second trial the rate was 8 oz per acre at petal-fall followed by 8 oz per acre at walnut size.


EXPERIMENTAL DESIGN AND ASSESSMENT OF FRUIT SIZE

In the majority of the trials the experimental plots were 5-10 acre treated and untreated blocks. Twenty trees were selected at random in each block and the diameters of 20 fruit measured per tree, using a straptype caliper. The field trials conducted in Clewiston, FL and Yuma, AZ were based on randomized block designs with 6-9 blocks per treatment. Four to 10 trees were selected within each block for determining fruit size, yield and juice quality.

In the mandarin trials in California two entire rows (30 trees per row) within 11 acre blocks were treated with Crop-Set™ and 20 trees selected at random within treated and untreated rows in these blocks. Two buffer rows were left between treated and untreated rows. As the mandarin trees were only 3 years old and produced light crops, only 10 fruit per tree were measured to assess fruit size. Statistical analysis was conducted using Duncan’s Multiple Range Test at P = 0.05.


Results and discussion

GRAPEFRUIT

At the trial site in Ft. Pierce, Crop-Set™ increased the yield of Marsh grapefruit in size class 27 to ≥23 by 35.2% (Table 1). The untreated trees produced 35.5% more fruit in the smaller size class 32-40. Crop-Set™ increased the fruit size of Ruby Red grapefruit in the size classes 40-48 and 23-27 by 8% and 5%, respectively. White grapefruit selections generally produce larger fruit than pigmented selections. Certain overseas markets prefer larger grapefruit; and the increase in total percentage of larger fruit in both selections increases the value of the crop significantly.


SWEET ORANGES

Crop-Set™ increased the percentage of Valencia fruit in size class 56-72 at the Ft. Pierce site by 21% (Table 2). Untreated trees produced 21% more fruit in the smaller size category 88-105. At the Frostproof site Crop-Set™ increased the yield of Valencia fruit in size category 48-64 by 22.5% and untreated trees produced 19.5% more smaller fruit in size class 88- 105. The increase in fruit size in the Valencia trial at Clewiston was not as dramatic as at the previous two sites but was still fairly substantial viz. 10.2 % more fruit in size class 48-72. The untreated trees produced 10% more smaller fruit in size class 88-125.


Table 1. Effect of Crop-Set™ on fruit size distribution (% of total) of grapefruit selections in Florida.


^ab Means in a column without common superscripts differ (P=0.05).



Table 2. Effect of Crop-Set™ on fruit size distribution (% of total) of sweet orange varieties in Florida.


^ab Means in a column without common superscripts differ (P=0.05).



The increase in fruit size in the Hamlin trial in Clewiston was not as dramatic as in the Valencia trials.

Hamlin is a mid-season variety which produces smaller fruit than Valencia. Crop-Set ™ treated trees produced 5.8% more fruit in size class 48-72 and the untreated trees 5.9% more fruit in the smaller size class 88-125.


LEMONS

Lemon trees can produce from 1-3 crops per season depending on where they are grown. In the desert areas of California only one crop is produced owing to the harsh summer climate. In the coastal areas 3-4 crops can be produced annually. Because of the ‘monsoon-type’ climate in Arizona, lemons trees can also produce more than one crop. Citrus growers with lemon trees that produce multiple crops must increase the fruit size and yield of the crop which is most valuable to them. Timing of Crop-Set™ applications is therefore critical in this citrus variety.

This is also to the benefit of the grower as he can manipulate his trees to produce the crop desired to meet market needs and supply the best fruit when his competitors, e.g. Spain and Argentina, are not able to. In this particular trial, the best treatment appeared to be one application of 16 oz. of Crop-Set™ per acre at petal-fall compared with the standard recommendation of one application of 8 oz per acre at petal-fall, followed up by a second application at the same dosage rate (Table 3). Trees that received only one application of Crop-Set™ produced 18% more fruit in total yield than the untreated trees. These trees also produced 17% more fruit in the size class 75-95. The untreated trees produced 18% more fruit in the smaller size class 115-285.


MANDARINS

The trees in these trials were only 3 years old and were therefore not expected to respond to treatment to the same extent as mature trees. However, only one of the selections (No. 8) showed no enhanced fruit size, while the remaining three selections all reacted very favorably to Crop-Set™ (Table 4). Not only did these selections show enhanced fruit size, but all four selections showed increased Brix levels.

The Brix values for the different selections treated with Crop-Set™ increased by 1%, 1.2%, 2.9% and 4.5%, respectively for selections No. 11, No. 8, No. 16 and No. 10. The fruit size increases for selections No. 10, No. 11 and No. 16 were 14.5% in size class > 60, 21% in size class 81-105, and 62% in size class 60-81, respectively. Untreated trees produced significantly more fruit in the smaller size classes.


Table 3. Effect of Crop-Set™ on fruit size distribution (% of total) of Lisbon lemon in Yuma, Arizona.


*Denotes one application of Crop-Set™ at 16 oz per acre at petal-fall.
^ab Means in a column without common superscripts differ (P=0.05).



Table 4. Effect of Crop-Set™ on fruit size distribution (% of total) of different mandarin selections in California.


^ab Means in a column without common superscripts differ (P=0.05).



Table 5. Effect of Crop-Set™ on fruit size distribution (% of total) and quality of Minneola tangelo in Yuma, AZ.


^ab Means in a column without common superscripts differ (P=0.05).



MINNEOLA TANGELOS

Minneola tangelo trees in Florida, California and Arizona tend to exhibit alternate bearing characteristics. This means that one year the crop is very light and the next year a large crop may be produced. The active ingredient in Crop-Set™ viz.

saponin, has the ability to enhance flower initiation in plants and should therefore be able to eliminate or reduce the alternate bearing characteristic of this variety if applied at the crucial time. The orchard currently under investigation received a third application of Crop-Set™ immediately following harvest to establish whether we could induce the trees to produce as good or even better crops during the 2004 season.

The application of Crop-Set™ during the 2003 season increased the overall yield of these trees by 29% and also increased the fruit in size class 40-56 by 58% (Table 5). Crop-Set™ application also increased juice content, solids:acids ratio and decreased peel thickness, though not significantly.

References

Balansard, J. and F. Pelliseur. 1943. Action de diverse saponines sur le bouturage épihylle de quelques Bégoniacées. Soc. Biol. Mars. 137:454.

Balansard, J. and F. Pelliseur. 1943. Action de saponine du Quillaya sur le pouvoir absorbant des graines de Pisum. Soc. Biol. Mars. 137:455.

Balansard, J. and F. Pelliseur. 1943. Action sur les germes de Blé isolés de la saponine du Quillaya. Soc. Biol. Mars. 137:461.

Balansard, J. and F. Pelliseur. 1943. Les saponines de Quillaya et Polygala agents de prolifération cellulaire. Soc. Biol. Mars. 137:523.

Balansard, J. and F. Pelliseur. 1943. Action des saponines sur l’ édification du pigment chlorophyllien. Soc. Biol. Mars. 137:763.

Balansard, J. and F. Pelliseur. 1944. L’action des saponines sur la croissance influence du traitement des semences sur les dernières phase de la végétation. Soc. Biol. Mars. 138:622.

Balansard, J. and F. Pelliseur. 1945. Saponines et croissance chez Solanum Lycopersicum L. Soc. Biol. Mars. 139:1098-1100.

Jameson, P. 2000. Cytokinins and auxins in plantpathogen interactions - An overview. Plant Growth Regulation 32:369-380.

Medina, C.L. 2003. Comparative effects of gibberellic acid, Crop-Set™ and potassium nitrate on vegetative development, fruit set and quality of orange fruits, Citrus sinensis (L.) Osbeck. In: Nutritional Biotechnology in the Feed and Food Industries, Proceedings of Alltech’s 19th Annual Symposium, Lexington, KY. Nottingham University Press, Nottingham, UK, pp. 407-414.

Zhang, X. and R. Schmidt. 1999. Biostimulating turf grasses. Grounds Maintenance 11:15-32.

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